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

.github/workflows/build-test.yml

@@ -42,7 +42,9 @@ jobs:
 
   build-linux:
     runs-on: ubuntu-latest
-    container: ${{ matrix.container }}
+    container:
+      image: ${{ matrix.container }}
+      options: --security-opt seccomp=unconfined
     name: Build (${{ matrix.name }})
     strategy:
       fail-fast: false
@@ -68,14 +70,17 @@ jobs:
             packageManager: dnf
 
     steps:
-      - name: Enable EPEL
-        run: dnf upgrade --refresh -y && dnf install -y epel-release epel-next-release
-        if: ${{ startsWith(matrix.name, 'CentOS')  }}
+      - name: Enable EPEL and CRB for CentOS
+        run: |
+          dnf upgrade --refresh -y
+          dnf install -y epel-release epel-next-release
+          dnf config-manager --set-enabled crb
+        if: ${{ startsWith(matrix.name, 'CentOS') }}
       - name: Install Prerequisites using dnf
-        run: dnf makecache --refresh && dnf install -y findutils libicu libdeflate-devel zstd libargon2-devel
+        run: dnf makecache --refresh && dnf install -y findutils libicu libdeflate-devel zstd libargon2-devel liburing-devel
         if: ${{ matrix.packageManager == 'dnf' }}
       - name: Install Prerequisites using apt
-        run: apt-get update -y && apt-get install -y curl libicu-dev libdeflate-dev zstd libargon2-dev tzdata
+        run: apt-get update -y && apt-get install -y curl libicu-dev libdeflate-dev zstd libargon2-dev tzdata liburing-dev
         if: ${{ matrix.packageManager == 'apt' }}
       - uses: actions/checkout@v4
         with: