community[patch]: GPTCache pydantic validation error on lookup (#19427)

Description:
this change fixes the pydantic validation error when looking up from
GPTCache, the `ChatOpenAI` class returns `ChatGeneration` as response
which is not handled.
use the existing `_loads_generations` and `_dumps_generations` functions
to handle it

Trace
```
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/development/scripts/chatbot-postgres-test.py", line 90, in <module>
    print(llm.invoke("tell me a joke"))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 166, in invoke
    self.generate_prompt(
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 544, in generate_prompt
    return self.generate(prompt_messages, stop=stop, callbacks=callbacks, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 408, in generate
    raise e
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 398, in generate
    self._generate_with_cache(
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/langchain_core/language_models/chat_models.py", line 585, in _generate_with_cache
    cache_val = llm_cache.lookup(prompt, llm_string)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/langchain_community/cache.py", line 807, in lookup
    return [
           ^
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/langchain_community/cache.py", line 808, in <listcomp>
    Generation(**generation_dict) for generation_dict in json.loads(res)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/langchain_core/load/serializable.py", line 120, in __init__
    super().__init__(**kwargs)
  File "/home/theinhumaneme/Documents/NebuLogic/conversation-bot/venv/lib/python3.11/site-packages/pydantic/v1/main.py", line 341, in __init__
    raise validation_error
pydantic.v1.error_wrappers.ValidationError: 1 validation error for Generation
type
  unexpected value; permitted: 'Generation' (type=value_error.const; given=ChatGeneration; permitted=('Generation',))
```


Although I don't seem to find any issues here, here's an
[issue](zilliztech/GPTCache#585) raised in
GPTCache. Please let me know if I need to do anything else

Thank you

---------

Co-authored-by: Bagatur <[email protected]>

libs/community/langchain_community/cache.py

@@ -811,11 +811,7 @@ def lookup(self, prompt: str, llm_string: str) -> Optional[RETURN_VAL_TYPE]:
  _gptcache = self._get_gptcache(llm_string)
 
  res = get(prompt, cache_obj=_gptcache)
- if res:
- return [
- Generation(**generation_dict) for generation_dict in json.loads(res)
- ]
- return None
+ return _loads_generations(res) if res is not None else None
 
  def update(self, prompt: str, llm_string: str, return_val: RETURN_VAL_TYPE) -> None:
  """Update cache.
@@ -831,7 +827,7 @@ def update(self, prompt: str, llm_string: str, return_val: RETURN_VAL_TYPE) -> N
  from gptcache.adapter.api import put
 
  _gptcache = self._get_gptcache(llm_string)
- handled_data = json.dumps([generation.dict() for generation in return_val])
+ handled_data = _dumps_generations(return_val)
  put(prompt, handled_data, cache_obj=_gptcache)
  return None