swallow shutdown exceptions in event deliverer stop if they're probably shutdown related

[rolfyone]

This can happen during building, and can be noisy.

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

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Note

AsyncEventDeliverer.stop() now swallows expected shutdown exceptions with debug logging and warns only on unexpected errors.

• Infrastructure / Events:
  • AsyncEventDeliverer.stop(): Wraps SafeFuture.allOf(...) with exceptionally to:
    • Detect root cause via Throwables.getRootCause.
    • Log RejectedExecutionException, CancellationException, and InterruptedException at debug level.
    • Log other exceptions at warn level.

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