fix(mistralai): timeout and connection errors are not classified as model errors

### Submission checklist - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [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). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [x] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs _No response_ ### Reproduction Steps / Example Code (Python) ```python import httpx from langchain_core.exceptions import ModelError, ModelTimeoutError from langchain_mistralai import ChatMistralAI class FailingClient: def post(self, **kwargs): raise httpx.ConnectTimeout( "timed out", request=httpx.Request("POST", "https://api.mistral.ai") ) model = ChatMistralAI(model="mistral-small", api_key="k", max_retries=0) model.client = FailingClient() try: model.invoke("hi") except ModelError: print("caught as ModelError") except httpx.TimeoutException as e: print(f"escaped as plain httpx: {type(e).__name__}") ``` ### Error Message and Stack Trace (if applicable) ```shell escaped as plain httpx: ConnectTimeout No traceback — the problem is that the exception is not classified, so `except …