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/Server.csproj

@@ -21,12 +21,12 @@
         <Delete Files="..\..\Distribution\$(AssemblyName).runtimeconfig.json" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\ModernUO.Serialization.Annotations.dll" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\CommunityToolkit.HighPerformance.dll" ContinueOnError="true" />
-        <Delete Files="..\..\Distribution\PollGroup.dll" ContinueOnError="true" />
+        <Delete Files="..\..\Distribution\IORingGroup.dll" ContinueOnError="true" />
+        <Delete Files="..\..\Distribution\ioring.dll" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\ref\$(AssemblyName).dll" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\Serilog.dll" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\Serilog.Sinks.Async.dll" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\Serilog.Sinks.Console.dll" ContinueOnError="true" />
-        <Delete Files="..\..\Distribution\wepoll.dll" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\LibDeflate.Bindings.dll" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\libdeflate.dll" ContinueOnError="true" />
         <Delete Files="..\..\Distribution\libdeflate.dylib" ContinueOnError="true" />
@@ -34,9 +34,9 @@
     </Target>
     <ItemGroup>
         <ProjectReference Include="..\Logger\Logger.csproj" />
+        <PackageReference Include="IORingGroup" Version="1.0.0" />
         <PackageReference Include="CommunityToolkit.HighPerformance" Version="8.4.0" />
         <PackageReference Include="LibDeflate.Bindings" Version="1.0.2.120" />
-        <PackageReference Include="PollGroup" Version="1.7.1" />
         <PackageReference Include="System.IO.Hashing" Version="10.0.2" />
 
         <PackageReference Include="ModernUO.Serialization.Annotations" Version="2.14.0" />