class_docstr: Worker extension for spans support
class_docstr_tok: ["Worker","extension","for","spans","support"]
code: def __init__(self, worker: Worker):
      self.worker = worker
      self.digests_total_since_heartbeat = {}
  
imports: from __future__ import annotations
  import uuid
  import weakref
  from collections import defaultdict
  from collections.abc import Hashable, Iterable, Iterator
  from contextlib import contextmanager
  from itertools import islice
  from typing import TYPE_CHECKING, Any
  import dask.config
  from dask.typing import Key
  from distributed.collections import sum_mappings
  from distributed.itertools import ffill
  from distributed.metrics import time
label_desc: Use image node_id 1 to create a new SpansWorkerExtension object  with example: obj = SpansWorkerExtension(worker)