This commit addresses the mysterious connection drops that occur under heavy load.
1. Added `TCPSendMutex` to `TCPSend` in `VehicleEvent.cpp`.
While `UDPSend`, `GameSend`, and `CoreSend` all had dedicated mutexes, `TCPSend` was missing one. This allowed the background `AutoPing` thread to occasionally collide with the main event loop while sending data. This interleaving corrupted the TCP headers, causing the server to instantly terminate the connection due to malformed packets. `TCPSend` is now safely locked with a `std::scoped_lock`.
