class_docstr: For saving and loading cache to a pickle file.
code: def save(self, data: dict[CacheKey, Any]):
      with open(self._cache_path, "wb") as fd:
          pickle.dump(data, fd)
  
imports: from collections.abc import Callable, Iterable
  import os
  import pickle
  import threading
  from typing import Any, Optional, Union
  from absl import logging
  from lit_nlp.api import dataset
  from lit_nlp.api import model
  from lit_nlp.api import types
  from lit_nlp.lib import serialize
label_desc: Use image node_id 2 for calling the PickleCacheLoader obj's underlying member method code with example usage: obj.save(data) without return types