Addressing inference timeout issues on inference operator tests

[pmpailis]

There seems be a race condition for when an inference request fails. Assume the following scenario:

When a bulk inference operation fails, completeIfFinished() invokes the completion listener under the checkpoint lock, which releases the request iterator and its backing input block (via ActionListener.releaseBefore(requests, listener) in performAsync). Then, the driver thread keeps polling the re-queued operation via pollNextRequest(), which checks hasFailure() || completed.get() before acquiring the checkpoint lock, so the check could be stale:

E.g.:

1. Driver thread passes the guard (no failure yet) and blocks on synchronized (checkpoint).
2. A response thread fails the operation, takes the lock, releases the block, releases the lock.
3. Driver thread acquires the lock and calls requestItemIterator.next() on the released block.

Reading the released block trips a MockBigArrays assertion on the driver thread. Since that's an AssertionError (not caught by performAsync's catch (Exception e)), it kills the driver and the operation never completes, which the test observes as a timeout.

So in this PR, we simply reuse the check outside the lock, to ensure that the operation is still valid.

Closes #154866

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[elasticsearchmachine]

Hi @pmpailis, I've created a changelog YAML for you.

[github-actions]

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[github-actions]

ℹ️ Important: Docs version tagging

👋 Thanks for updating the docs! Just a friendly reminder that our docs are now cumulative. This means all 9.x versions are documented on the same page and published off of the main branch, instead of creating separate pages for each minor version.

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[mayya-sharipova]

shoudl we remove mention of the issue here: "#154866" and keep comment general overall.

[mayya-sharipova]

The fix LGTM, but I am not an expert in this area!