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/UOContent/Misc/ServerList.cs

@@ -79,14 +79,14 @@ namespace Server.Misc
             {
                 var ns = e.State;
 
-                var ipep = (IPEndPoint)ns.Connection?.LocalEndPoint;
-                if (ipep == null)
+                var localEndPoint = ns.LocalEndPoint;
+                if (localEndPoint == null)
                 {
                     return;
                 }
 
-                var localAddress = ipep.Address;
-                var localPort = ipep.Port;
+                var localAddress = localEndPoint.Address;
+                var localPort = localEndPoint.Port;
 
                 if (_useServerListingAddressConfig)
                 {
@@ -94,9 +94,8 @@ namespace Server.Misc
                 }
                 else if (localAddress.IsPrivateNetwork())
                 {
-                    ipep = (IPEndPoint)ns.Connection.RemoteEndPoint;
-
-                    if (ipep == null || !ipep.Address.IsPrivateNetwork() && _publicAddress != null)
+                    // Check if client is from a public network
+                    if (!ns.Address.IsPrivateNetwork() && _publicAddress != null)
                     {
                         localAddress = _publicAddress;
                     }

Projects/UOContent/Network/Packets/IncomingAccountPackets.cs

@@ -384,7 +384,6 @@ public static class IncomingAccountPackets
 
             // Comment out these lines to turn off huffman compression
             state.CompressionEnabled = true;
-            state.PacketEncoder ??= NetworkCompression.Compress;
 
             state.SendSupportedFeature();
             state.SendCharacterList();

Projects/UOContent/Special Systems/Engines/PreventInaccess.cs

@@ -69,7 +69,7 @@ namespace Server.Misc
             }
         }
 
-        private static bool HasDisconnected(Mobile m) => m.NetState?.Connection == null;
+        private static bool HasDisconnected(Mobile m) => m.NetState is not { IsConnected: true };
 
         private static LocationInfo GetRandomDestination() => m_Destinations.RandomElement();