Add TcpRpc server and client and split crypto code into multiple classes

Networking/TcpConnection.cs

@@ -0,0 +1,18 @@
+using System.Net.Sockets;
+
+/// <summary>
+/// Simple wrapper around TcpClient to hold connection-scoped resources safely.
+/// </summary>
+public class TcpConnection(TcpClient client) : IDisposable
+{
+    public TcpClient Client { get; } = client;
+    public NetworkStream Stream { get; } = client.GetStream();
+    public SemaphoreSlim SendLock { get; } = new(1, 1);
+
+    public void Dispose()
+    {
+        Stream.Dispose();
+        Client.Dispose();
+        SendLock.Dispose();
+    }
+}