code: def add_ephemeral_listener(self, callback, event_type=None):
          
          listener_id = uuid4()
          self.ephemeral_listeners.append(
              {
                  'uid': listener_id,
                  'callback': callback,
                  'event_type': event_type
              }
          )
          return listener_id
docs: Add a callback handler for ephemeral events going to this room.
  
          Args:
              callback (func(room, event)): Callback called when an ephemeral event arrives.
              event_type (str): The event_type to filter for.
          Returns:
              uuid.UUID: Unique id of the listener, can be used to identify the listener.