Repository: langchain
Issue: Pydantic validation error on angchain_community.chat_models.ChatLiteLLMRouter
Labels: 🤖:bug

### 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

ChatLiteLLMRouter
```python
from langchain_core.prompts import ChatPromptTemplate
from litellm.router import Router
from langchain_community.chat_models import ChatLiteLLMRouter

_prompt = ChatPromptTemplate.from_messages(
    [
        ("human", "You are an asistant. {input}"),
    ]
)


model_list = [
    {
        "model_name": "claude_3_haiku",
        "litellm_params": {
            "model": "bedrock/anthropic.claude-3-haiku-20240307-v1:0",
        },
    },
    {
        "model_name": "claude_3_sonnet",
        "litellm_params": {
            "model": "bedrock/anthropic.claude-3-sonnet-20240229-v1:0",
        },
    },
]

litellm_router = Router(model_list=model_list)
_modellm=ChatLiteLLMRouter(router=litellm_router)
```

### Error Message and Stack Trace (if applicable)

pydantic_core._pydantic_core.ValidationError: 1 validation error for ChatLiteLLMRouter
router
  Field required [type=missing, input_value={'name': None, 'cache': N...ogether_ai_api_key': ''}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.9/v/missing

### Description

I'm trying to create an instance of ChatLiteLLMRouter object, passing the required parameter router as:
```python
_modellm=ChatLiteLLMRouter(router=litellm_router)
```
expected:  the  ChatLiteLLMRouter object is created
actual: exception raised because do not detect router parameter being passed:
```python
pydantic_core._pydantic_core.ValidationError: 1 validation error for ChatLiteLLMRouter
router
Field required [type=missing, input_value={'name': None, 'cache': N...ogether_ai_api_key': ''}, input_type=dict]
For further information visit https://errors.pydantic.dev/2.9/v/missing
```
### System Info


System Information
------------------
> OS:  Linux
> OS Version:  #1 SMP Wed Mar 2 00:30:59 UTC 2022
> Python Version:  3.11.10 (main, Sep  7 2024, 18:35:41) [GCC 11.4.0]

Package Information
-------------------
> langchain_core: 0.3.12
> langchain: 0.3.3
> langchain_community: 0.3.2
> langsmith: 0.1.136
> langchain_aws: 0.2.2
> langchain_cli: 0.0.31
> langchain_text_splitters: 0.3.0
> langserve: 0.3.0

Optional packages not installed
-------------------------------
> langgraph

Other Dependencies
------------------
> aiohttp: 3.10.10
> async-timeout: Installed. No version info available.
> boto3: 1.35.43
> dataclasses-json: 0.6.7
> fastapi: 0.115.2
> gitpython: 3.1.43
> gritql: 0.1.5
> httpx: 0.27.2
> jsonpatch: 1.33
> langserve[all]: Installed. No version info available.
> numpy: 1.26.4
> orjson: 3.10.7
> packaging: 24.1
> pydantic: 2.9.2
> pydantic-settings: 2.6.0
> PyYAML: 6.0.2
> requests: 2.32.3
> requests-toolbelt: 1.0.0
> SQLAlchemy: 2.0.36
> sse-starlette: 1.8.2
> tenacity: 8.5.0
> tomlkit: 0.12.5
> typer[all]: Installed. No version info available.
> typing-extensions: 4.12.2
> uvicorn: 0.23.2