Sends a shutdown signal to the unity environment, and closes the grpc connection.

def close(self):
        """
        Sends a shutdown signal to the unity environment, and closes the grpc connection.
        """
        if self.is_open:
            message_input = UnityMessage()
            message_input.header.status = 400
            self.unity_to_external.parent_conn.send(message_input)
            self.unity_to_external.parent_conn.close()
            self.server.stop(False)
            self.is_open = False