refactor: improve multiplayer connection lifecycle

* Move client/server connection handling into game-specific networking classes
* Add multiplayer data reset for disconnected clients
* Clean up invalid MessageBus listeners after disconnects
* Persist lobby host address and port in game data
* Standardize the default server port to 8080
* Increase server address input length to support valid addresses
* Remove obsolete connection and match initialization logic from base networking

globals/message_bus.gd

@@ -11,6 +11,14 @@ func subscribe(id: String, callback: Callable) -> void:
 	message_types.get(id).append(callback)
 
 
+func clear_voided_listeners() -> void:
+	for mtype in message_types.keys():
+		var mlisteners: Array = message_types.get(mtype)
+		for mlistener in mlisteners:
+			if mlistener.is_valid(): continue
+			mlisteners.erase(mlistener)
+
+
 func emit_local(id: String, data: Variant, expand: bool = false) -> void:
 	emit_propagation(id, data, expand)