Mistral integration does not properly handle retries and concurrency limits

### Checked other resources - [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 asyncio from langchain_mistralai import ChatMistralAI async def test_concurrency(): llm = ChatMistralAI(max_concurrent_requests=2) async def call(): return await llm.ainvoke("Hello") # Fire multiple requests await asyncio.gather(*(call() for _ in range(5))) asyncio.run(test_concurrency()) ``` ### Error Message and Stack Trace (if applicable) ```shell ``` ### Description The current Mistral integration does not properly enforce retry behavior and concurrency limits. Expected behavior: - Retries should only occur for transient errors (e.g., 429, 5xx, network failures) - Concurrency should be limited by max_concurrent_requests Actual behavior: - Retry logic applies broadly without filtering retryable errors - Async calls us…