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/ContainerPacketTests.cs

@@ -7,7 +7,6 @@ namespace Server.Tests.Network;
 [Collection("Sequential Server Tests")]
 public class ContainerPacketTests
 {
-
     [Fact]
     public void TestContainerDisplay()
     {
@@ -19,7 +18,7 @@ public class ContainerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendDisplayContainer(serial, gumpId);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -35,7 +34,7 @@ public class ContainerPacketTests
         ns.ProtocolChanges = ns.ProtocolChanges | ProtocolChanges.ContainerGridLines | ProtocolChanges.HighSeas;
         ns.SendDisplayContainer(serial, gumpId);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -49,7 +48,7 @@ public class ContainerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendDisplaySpellbook(serial);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -64,7 +63,7 @@ public class ContainerPacketTests
         ns.ProtocolChanges = ns.ProtocolChanges | ProtocolChanges.ContainerGridLines | ProtocolChanges.HighSeas;
         ns.SendDisplaySpellbook(serial);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -85,7 +84,7 @@ public class ContainerPacketTests
         ns.SendSpellbookContent(serial, graphic, offset, content);
         ObjectPropertyList.Enabled = opl;
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -102,7 +101,7 @@ public class ContainerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendSpellbookContent(serial, graphic, offset, content);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -120,7 +119,7 @@ public class ContainerPacketTests
         ns.ProtocolChanges |= ProtocolChanges.ContainerGridLines;
         ns.SendSpellbookContent(serial, graphic, offset, content);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -135,7 +134,7 @@ public class ContainerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendContainerContentUpdate(item);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -151,7 +150,7 @@ public class ContainerPacketTests
         ns.ProtocolChanges |= ProtocolChanges.ContainerGridLines;
         ns.SendContainerContentUpdate(item);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -172,7 +171,7 @@ public class ContainerPacketTests
         using var ns = PacketTestUtilities.CreateTestNetState();
         ns.SendContainerContent(m, cont);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 
@@ -194,7 +193,7 @@ public class ContainerPacketTests
         ns.ProtocolChanges |= ProtocolChanges.ContainerGridLines;
         ns.SendContainerContent(m, cont);
 
-        var result = ns.SendPipe.Reader.AvailableToRead();
+        var result = ns.SendBuffer.GetReadSpan();
         AssertThat.Equal(result, expected);
     }
 }