fix(chroma): reject async chroma clients with a clear error

[lakshayt7]

Fixes #30704

Summary

Reject awaitable Chroma clients passed to langchain_chroma.Chroma with a clear TypeError instead of failing later with an AttributeError.

Why

Passing chromadb.AsyncHttpClient(...) currently produces an awaitable, and Chroma later crashes during collection setup with 'coroutine' object has no attribute 'get_or_create_collection'. This change fails fast with an actionable message that points users to a synchronous client.

Changes

• validate client during Chroma initialization
• raise a clear TypeError when an awaitable client is provided
• add a regression test for chromadb.AsyncHttpClient(...)

Testing

• pytest tests/unit_tests/test_vectorstores.py -q

AI Disclosure

This PR was prepared with assistance from an AI coding agent, then reviewed and submitted by me.

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