`ChatGroq` accepts `n > 1` for non-streaming requests although Groq only supports `n=1

### 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 - [x] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-typesafe - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs I did not find an existing issue or PR for this exact problem. ### Reproduction Steps / Example Code (Python) ```python import os import groq from langchain_groq import ChatGroq if "GROQ_API_KEY" not in os.environ: raise RuntimeError("Set GROQ_API_KEY before running this script") # Use a model that is available to the reporting account. model = os.getenv("GROQ_MODEL", "openai/gpt-oss-20b") # Control: the supported value works with the same key, model, and environment. control = ChatGroq(model=model, n=1, max_retries=0) print("n=1 response:", control.invoke("Reply with exactly: hi").content) # Bug: this invalid provider configuration is accepted locally. subject = ChatGroq(model=model, n=2, max_retries=0) print("ChatGroq constructed with n=", subject.n) try: subject.invoke("Reply with exactly…