fix: Fixes networking issues (#1958)

### Summary
- Puts back `EventSink.SocketConnect`.
- Reverts networking change to push the networking to a separate thread.
- Reverts changes to the firewall by removing the firewall queue.
- Fixes listeners not shutting down with the server.
- Fixes race condition causing connections to get stuck even after they are disposed.

> [!NOTE]
> **Developer Note**
> Networking has been reverted back to using the main thread instead of a background thread. This alleviated complexity and the requirement for concurrent queues all over the place.

Projects/Server/Events/SocketConnectionEvent.cs

@@ -0,0 +1,41 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2023 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: SocketConnectionEvent.cs                                        *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Net.Sockets;
+using System.Runtime.CompilerServices;
+
+namespace Server;
+
+public class SocketConnectEventArgs
+{
+    public SocketConnectEventArgs(Socket c)
+    {
+        Connection = c;
+        AllowConnection = true;
+    }
+
+    public Socket Connection { get; }
+
+    public bool AllowConnection { get; set; }
+}
+
+public static partial class EventSink
+{
+    public static event Action<SocketConnectEventArgs> SocketConnect;
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void InvokeSocketConnect(SocketConnectEventArgs e) => SocketConnect?.Invoke(e);
+}