fix: handle inverted index worker exits during dispatch

[BubbleCal]

this drops all receivers if all workers have failed, so that dispatching can be stopped

[github-actions]

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[github-actions]

PR Review

Good fix — the old code would panic (expect("failed to send batch")) when a worker exited early due to an error because the receiver side was dropped. Replacing that with a graceful is_err() check + break and then propagating the real worker error via index_task.await?? is the right approach. The drop(receiver) after spawning ensures the channel lifetime is properly tied to the workers. Test coverage looks solid.

One nit:

Typo in comment (builder.rs): "this only happens if all workers have existed" → should be "exited".

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rust/lance-index/src/scalar/inverted/builder.rs	85.71%	4 Missing ⚠️

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