class_docstr: Extend Dask's Client with handlers to handle PubSub machinery
code: def __init__(self, client):
      self.client = client
      self.client._stream_handlers.update(
          {"pubsub-msg": self.handle_message}
      )
  
      self.subscribers = defaultdict(weakref.WeakSet)
  
imports: from __future__ import annotations
  import asyncio
  import logging
  import threading
  import weakref
  from collections import defaultdict, deque
  from dask.utils import parse_timedelta
  from distributed.core import CommClosedError
  from distributed.metrics import time
  from distributed.protocol.serialize import to_serialize
  from distributed.utils import TimeoutError, sync, wait_for
label_desc: Use image node_id 1 to create a new PubSubClientExtension object  with example: obj = PubSubClientExtension(client)