core[patch]: Fix logic in BaseChatModel that processes the llm string that is used as a key for caching chat models responses (#23842)
This PR should fix the following issue:
https://github.com/langchain-ai/langchain/issues/23824
Introduced as part of this PR:
https://github.com/langchain-ai/langchain/pull/23416
I am unable to reproduce the issue locally though it's clear that we're
getting a `serialized` object which is not a dictionary somehow.
The test below passes for me prior to the PR as well
```python
def test_cache_with_sqllite() -> None:
from langchain_community.cache import SQLiteCache
from langchain_core.globals import set_llm_cache
cache = SQLiteCache(database_path=".langchain.db")
set_llm_cache(cache)
chat_model = FakeListChatModel(responses=["hello", "goodbye"], cache=True)
assert chat_model.invoke("How are you?").content == "hello"
assert chat_model.invoke("How are you?").content == "hello"
```