Repository: langchain
Issue: Cache de-serialization does not work on ChatOpenAI with structured output, Pydantic classes and json_schema
Labels: 🤖:bug,investigate

### Checked other resources

- [X] I added a very descriptive title to this issue.
- [X] I searched the LangChain documentation with the integrated search.
- [X] I used the GitHub search to find a similar question and didn't find it.
- [X] I am sure that this is a bug in LangChain rather than my code.
- [X] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

### Example Code

```python
from langchain.globals import set_llm_cache
from langchain_community.cache import SQLiteCache
from langchain_openai import ChatOpenAI
from pydantic import BaseModel

set_llm_cache(SQLiteCache())

class Temperature(BaseModel):
    value: int
    city: str

chat = ChatOpenAI(model="gpt-4o").with_structured_output(Temperature, method="json_schema")

chat.invoke("What is the average temperature of Rome in May?")
# on this second call the exception is raised
chat.invoke("What is the average temperature of Rome in May?")
```

### Error Message and Stack Trace (if applicable)

```
Retrieving a cache value that could not be deserialized properly. This is likely due to the cache being in an older format. Please recreate your cache to avoid this error.
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/berardi/Library/Caches/pypoetry/virtualenvs/langchain-elasticsearch-IgW_j1SW-py3.10/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 3020, in invoke
    input = context.run(step.invoke, input, config, **kwargs)
  File "/Users/berardi/Library/Caches/pypoetry/virtualenvs/langchain-elasticsearch-IgW_j1SW-py3.10/lib/python3.10/site-packages/langchain_core/runnables/base.py", line 5352, in invoke
    return self.bound.invoke(
  File "/Users/berardi/Library/Caches/pypoetry/virtualenvs/langchain-elasticsearch-IgW_j1SW-py3.10/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 286, in invoke
    self.generate_prompt(
  File "/Users/berardi/Library/Caches/pypoetry/virtualenvs/langchain-elasticsearch-IgW_j1SW-py3.10/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 786, in generate_prompt
    return self.generate(prompt_messages, stop=stop, callbacks=callbacks, **kwargs)
  File "/Users/berardi/Library/Caches/pypoetry/virtualenvs/langchain-elasticsearch-IgW_j1SW-py3.10/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 643, in generate
    raise e
  File "/Users/berardi/Library/Caches/pypoetry/virtualenvs/langchain-elasticsearch-IgW_j1SW-py3.10/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 633, in generate
    self._generate_with_cache(
  File "/Users/berardi/Library/Caches/pypoetry/virtualenvs/langchain-elasticsearch-IgW_j1SW-py3.10/lib/python3.10/site-packages/langchain_core/language_models/chat_models.py", line 818, in _generate_with_cache
    return ChatResult(generations=cache_val)
  File "/Users/berardi/Library/Caches/pypoetry/virtualenvs/langchain-elasticsearch-IgW_j1SW-py3.10/lib/python3.10/site-packages/pydantic/main.py", line 214, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
pydantic_core._pydantic_core.ValidationError: 1 validation error for ChatResult
generations.0
  Input should be a valid dictionary or instance of ChatGeneration [type=model_type, input_value=Generation(text='{"lc": 1...id_tool_calls": []}}}}'), input_type=Generation]
    For further information visit https://errors.pydantic.dev/2.10/v/model_type
```

### Description

When using the specific configuration in the example, for ChatOpenAI structured output, caches won't work properly. 

The problem appears only with Pydantic classes and `"json_schema"`. For example, there is no problem when using `TypedDict` as schema, or when using `"function_calling"` as method. 

I have also tested Redis and Elasticsearch cache integrations. The issue is the same, LangChain is not able to restore the serialized output from the cache. I am aware of the [limits of load methods](https://python.langchain.com/docs/how_to/serialization/), the problem however is in the dumping phase, where a Pydantic object is [handled by this code](https://github.com/langchain-ai/langchain/blob/b258ff1930765da9bd0761ad47b1401c246a595a/libs/core/langchain_core/load/dump.py#L20). It cannot be properly serialized.

### System Info

System Information
------------------
> OS:  Darwin
> OS Version:  Darwin Kernel Version 24.2.0: Fri Dec  6 18:41:43 PST 2024; root:xnu-11215.61.5~2/RELEASE_X86_64
> Python Version:  3.11.7 (main, Jan 11 2024, 20:41:08) [Clang 13.0.0 (clang-1300.0.29.30)]

Package Information
-------------------
> langchain_core: 0.3.24
> langchain: 0.3.11
> langchain_community: 0.3.11
> langsmith: 0.2.3
> langchain_elasticsearch: 0.3.0
> langchain_openai: 0.2.12
> langchain_text_splitters: 0.3.2

Optional packages not installed
-------------------------------
> langserve

Other Dependencies
------------------
> aiohttp: 3.11.10
> async-timeout: Installed. No version info available.
> dataclasses-json: 0.6.7
> elasticsearch[vectorstore-mmr]: Installed. No version info available.
> httpx: 0.28.1
> httpx-sse: 0.4.0
> jsonpatch: 1.33
> langsmith-pyo3: Installed. No version info available.
> numpy: 1.26.4
> openai: 1.57.3
> orjson: 3.10.12
> packaging: 24.2
> pydantic: 2.10.3
> pydantic-settings: 2.7.0
> PyYAML: 6.0.2
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> SQLAlchemy: 2.0.36
> tenacity: 9.0.0
> tiktoken: 0.8.0
> typing-extensions: 4.12.2