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/PlayerPacketTests.cs

@@ -23,7 +23,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendStatLockInfo(m);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -38,7 +38,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendChangeUpdateRange((byte)range);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -50,7 +50,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendDeathStatus();
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -64,7 +64,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendDisplayProfile((Serial)serial, header, body, footer);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -78,7 +78,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendLiftReject(reason);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -90,7 +90,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendLogoutAck();
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -105,7 +105,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendWeather((byte)type, (byte)density, (byte)temp);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -120,7 +120,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendServerChange(p, map);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -135,7 +135,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendSequence(num);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -151,7 +151,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendLaunchBrowser(uri);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -175,7 +175,7 @@ public class PlayerPacketTests
             itemId, hue, amount
         );
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -189,7 +189,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendSeasonChange((byte)season, playSound);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -204,7 +204,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendDisplayPaperdoll((Serial)m, title, warmode, canLift);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -219,7 +219,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendPlayMusic(music);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -233,7 +233,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendScrollMessage(type, tip ,text);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -247,7 +247,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendCurrentTime(date);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -261,7 +261,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendPathfindMessage(p);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -276,7 +276,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendPingAck(ping);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -291,7 +291,7 @@ public class PlayerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendDisplayHuePicker(huePicker.Serial, huePicker.ItemID);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 }