fix: add ollama async timeout

[psschwei]

Pull Request

Issue

Fixes #650

Description

Adds an optional timeout parameter to OllamaModelBackend that's forwarded to both the sync and async Ollama clients (including the per-event-loop async clients created lazily by _async_client). When the Ollama server stalls under load, requests now fail fast instead of hanging indefinitely.

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code was added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

Attribution

• AI coding assistants used

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