Add messages to be managed by the leaser.

def add(self, items):
        """Add messages to be managed by the leaser."""
        for item in items:
            # Add the ack ID to the set of managed ack IDs, and increment
            # the size counter.
            if item.ack_id not in self._leased_messages:
                self._leased_messages[item.ack_id] = _LeasedMessage(
                    added_time=time.time(), size=item.byte_size
                )
                self._bytes += item.byte_size
            else:
                _LOGGER.debug("Message %s is already lease managed", item.ack_id)