docs: def _generate_ack_id(self, sid, namespace, callback):
          """Generate a unique identifier for an ACK packet."""
          namespace = namespace or '/'
          if sid not in self.callbacks:
              self.callbacks[sid] = {}
          if namespace not in self.callbacks[sid]:
              self.callbacks[sid][namespace] = {0: itertools.count(1)}
          id = six.next(self.callbacks[sid][namespace][0])
          self.callbacks[sid][namespace][id] = callback
          return id