[FLINK-39879][tests] Stop CheckpointAcknowledgeFailureITCase hanging on slow CI

[MartijnVisser]

What is the purpose of the change

CheckpointAcknowledgeFailureITCase.testCheckpointAckFailure can hang the entire surefire fork on a slow CI machine until the 900s no-output watchdog kills it (observed on master, build 75716). The test sets a deliberately tiny pekko.ask.timeout so the oversized checkpoint-ACK RPC times out (load-bearing for the AskTimeoutException assertion), but that timeout applies to every cluster RPC. On a slow agent an unrelated RPC (e.g. task deployment) can time out and fail the job terminally before the keyed state is updated, so the future the test waits on never completes and the unbounded wait wedges the fork.

This makes the wait fail fast with the real cause and adds a hard timeout so the test can never hang a fork again. It is a test-only stabilization; the assertion is unchanged.

Brief change log

• Propagate a terminal job failure into stateUpdatedFuture via a whenComplete handler on getJobExecutionResult() (unwrapping the CompletionException to the real cause), so the wait fails fast instead of blocking forever.
• executeJobAsync now returns the JobClient so the test can observe job termination.
• Add @Timeout(5, MINUTES) as the hard anti-hang guard (consistent with ApproximateLocalRecoveryDownstreamITCase in the same package).

Verifying this change

This change is a test stabilization of an existing test; the assertion (triggerCheckpoint(...) must throw CheckpointException caused by AskTimeoutException) is unchanged. Verified locally:

• Happy path passes: mvn -pl flink-tests -Dtest=CheckpointAcknowledgeFailureITCase test → Tests run: 1, Failures: 0.
• Fail-fast path: temporarily forcing the ask timeout very low so an unrelated RPC fails the job before the state update — the test now fails fast (~24s) with the job's real JobExecutionException instead of hanging until the watchdog kill.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no (test-only change)
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

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Was generative AI tooling used to co-author this PR?

• Yes (Claude Opus 4.8 (1M context))

Generated-by: Claude Opus 4.8 (1M context)

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CI report:

• 4efce2b Azure: SUCCESS

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