code: def add(self, items):
          
          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)
docs: Add messages to be managed by the leaser.