mistralai: update tool calling (#19451)

```python
from langchain.agents import tool
from langchain_mistralai import ChatMistralAI


llm = ChatMistralAI(model="mistral-large-latest", temperature=0)

@tool
def get_word_length(word: str) -> int:
    """Returns the length of a word."""
    return len(word)


tools = [get_word_length]
llm_with_tools = llm.bind_tools(tools)

llm_with_tools.invoke("how long is the word chrysanthemum")
```
currently raises
```
AttributeError: 'dict' object has no attribute 'model_dump'
```

Same with `.with_structured_output`
```python
from langchain_mistralai import ChatMistralAI
from langchain_core.pydantic_v1 import BaseModel

class AnswerWithJustification(BaseModel):
    """An answer to the user question along with justification for the answer."""
    answer: str
    justification: str

llm = ChatMistralAI(model="mistral-large-latest", temperature=0)
structured_llm = llm.with_structured_output(AnswerWithJustification)

structured_llm.invoke("What weighs more a pound of bricks or a pound of feathers")
```

This appears to fix.

libs/partners/mistralai/langchain_mistralai/chat_models.py

@@ -83,7 +83,7 @@ def _convert_mistral_chat_message_to_message(
 
     additional_kwargs: Dict = {}
     if tool_calls := _message.get("tool_calls"):
-        additional_kwargs["tool_calls"] = [tc.model_dump() for tc in tool_calls]
+        additional_kwargs["tool_calls"] = tool_calls
     return AIMessage(content=content, additional_kwargs=additional_kwargs)