fix: Adds back socket connected event

[kamronbatman]

Summary

Adds back the SocketConnected event. This event only fires asynchronously! (TcpServer thread).

Example:

public static void Configure()
{
    TcpServer.EventSink.SocketConnected += OnSocketConnected;
}

// WARNING: Executed on the TcpServer thread!
private static void OnSocketConnected(TcpServer.SocketConnectedEventArgs args)
{
    if (... logic here...)
    {
        AdminFirewall.Add(((IPEndPoint)Socket.RemoteEndPoint)!.Address);
    }
}