feat: Upgrades networking to use io_uring. (#2315)

> [!IMPORTANT]
> **Breaking Changes**
> - DecodePacket and EncodePacket delegates replaced with IClientEncryption interface
> - NetState.Connection (Socket) replaced with internal RingSocket management
> - NetState.RecvPipe and NetState.SendPipe removed (buffers managed internally)

## Summary

Upgrades the networking stack from PollGroup-based I/O to io_uring, significantly improving I/O performance on Linux.
This also adds native client encryption support for encrypted UO clients.

## Major Changes

io_uring Networking Architecture
- Replaced PollGroup with IORingGroup for async socket I/O operations
- Removed Pipe.cs (mirrored ring buffer) and TcpServer.cs in favor of RingSocketManager
- Added NetState.Network.cs - centralized network infrastructure handling accept, recv, send, and disconnect
completions
- Added SocketHelper.cs - platform-specific socket utilities for raw socket handle operations (getpeername,
getsockname)
- Buffer management now handled by RingSocketManager with configurable slab allocation

### Client Encryption Support
- Added full encryption stack in Network/Encryption/:
  - EncryptionConfig.cs - configurable encryption modes (None, Unencrypted, Encrypted, Both)
  - EncryptionManager.cs - encryption detection and initialization for login/game packets
  - LoginEncryption.cs - handles login packet encryption with version-derived keys
  - GameEncryption.cs - handles game server encryption using Twofish
  - TwofishEngine.cs - optimized Twofish block cipher implementation
  - LoginKeys.cs - encryption key table for client versions
  - IClientEncryption.cs - interface for client encryption implementations

### NetState Improvements
- Replaced Socket Connection with RingSocket _socket for managed socket lifecycle
- Changed from GCHandle polling to event-based completion processing
- Disconnect handling now properly waits for pending sends to flush
- Simplified connecting socket management using lazy queue removal

### Configuration
- New settings: network.encryptionMode and network.encryptionDebug
- Encryption mode flags: Unencrypted, Encrypted, or Both

### Dependencies
- Replaced PollGroup NuGet package with IORingGroup
- Linux requires liburing-dev / liburing-devel package

### Test plan

- Verify server starts and accepts connections on Linux with io_uring
- Verify server starts and accepts connections on Windows (fallback to IOCP)
- Test unencrypted client connections (ClassicUO with encryption disabled)
- Test encrypted client connections if available
- Verify graceful disconnect flushes pending data
- Confirm CI builds pass on all target platforms

Projects/Server.Tests/Tests/Network/Packets/Outgoing/MobilePacketTests.cs

@@ -17,7 +17,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendDeathAnimation(killed, corpse);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -32,7 +32,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendBondedStatus(petSerial, bonded);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -52,7 +52,7 @@ public class MobilePacketTests
 
         ns.SendMobileMoving(m, noto);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -70,7 +70,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileName(m);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -102,7 +102,7 @@ public class MobilePacketTests
             delay
         );
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -128,7 +128,7 @@ public class MobilePacketTests
             delay
         );
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -148,7 +148,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileHealthbar(m, Healthbar.Poison);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -169,7 +169,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileHealthbar(m, Healthbar.Yellow);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -192,7 +192,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileStatusCompact(m, canBeRenamed);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -225,7 +225,7 @@ public class MobilePacketTests
         var expected = new MobileStatus(beholder, beheld, ns).Compile();
         ns.SendMobileStatus(beholder, beheld);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -263,7 +263,7 @@ public class MobilePacketTests
         var expected = new MobileStatusExtended(m, ns).Compile();
         ns.SendMobileStatus(m, m);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
         Core.Expansion = oldExpansion;
         expansionInfo.MobileStatusVersion = oldVersion;
@@ -284,7 +284,7 @@ public class MobilePacketTests
         var expected = new MobileUpdate(m, ns.StygianAbyss).Compile();
         ns.SendMobileUpdate(m);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -339,7 +339,7 @@ public class MobilePacketTests
         var expected = new MobileIncoming(ns, beholder, beheld).Compile();
         ns.SendMobileIncoming(beholder, beheld);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -356,7 +356,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileHits(m);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -373,7 +373,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileHits(m, true);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -390,7 +390,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileMana(m);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -407,7 +407,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileMana(m, true);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -424,7 +424,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileStam(m);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -441,7 +441,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileStam(m, true);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -462,7 +462,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileAttributes(m);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -483,7 +483,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendMobileAttributes(m, true);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -496,7 +496,7 @@ public class MobilePacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendRemoveEntity(e);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 }