code: def start(self) -> None:
      self._thread.start()
  
imports: import concurrent.futures
  import functools
  import os
  import queue
  import shutil
  import threading
  from typing import TYPE_CHECKING, NamedTuple, Optional, Union, cast
  from wandb.filesync import step_upload
  from wandb.sdk.lib import filesystem, runid
  from wandb.sdk.lib.paths import LogicalPath
label_desc: Use image node_id 3 for calling the StepChecksum obj's underlying member method code with example usage: obj.start() without return types