Fix: Enable max_retries Parameter in ChatMistralAI Class (#30448)

**partners: Enable max_retries in ChatMistralAI**

**Description**

- This pull request reactivates the retry logic in the
completion_with_retry method of the ChatMistralAI class, restoring the
intended functionality of the previously ineffective max_retries
parameter. New unit test that mocks failed/successful retry calls and an
integration test to confirm end-to-end functionality.

**Issue**
- Closes #30362

**Dependencies**
- No additional dependencies required

Co-authored-by: andrasfe <andrasf94@gmail.com>

libs/partners/mistralai/langchain_mistralai/chat_models.py

@@ -464,9 +464,9 @@ class ChatMistralAI(BaseChatModel):
         self, run_manager: Optional[CallbackManagerForLLMRun] = None, **kwargs: Any
     ) -> Any:
         """Use tenacity to retry the completion call."""
-        # retry_decorator = _create_retry_decorator(self, run_manager=run_manager)
+        retry_decorator = _create_retry_decorator(self, run_manager=run_manager)
 
-        # @retry_decorator
+        @retry_decorator
         def _completion_with_retry(**kwargs: Any) -> Any:
             if "stream" not in kwargs:
                 kwargs["stream"] = False