Start monitoring the base unit.

def start(self) -> None:
        """
        Start monitoring the base unit.
        """

        self._shutdown = False

        # Start listening (if server) / Open connection (if client)
        if isinstance(self._protocol, Server):
            self.create_task(self._async_listen)
        elif isinstance(self._protocol, Client):
            self.create_task(self._async_open)
        else:
            raise NotImplementedError