[fix][test] Fix flaky TestReplicationWorker.testRepairedNotAdheringPlacementPolicyLedgerFragmentsOnRack

[lhotari]

Fixes #26307

Motivation

TestReplicationWorker.testRepairedNotAdheringPlacementPolicyLedgerFragmentsOnRack failed both TestNG
attempts in this CI - Unit - Pulsar Metadata run,
on assertNotNull(stat). The shared helper testRepairedNotAdheringPlacementPolicyLedgerFragments(...)
that backs it (and testReplicationStats) has two independent timing problems.

1. The underreplication mark is read before it is written.

AuditorPlacementPolicyCheckTask.doPlacementPolicyCheck() fires
ledgerUnderreplicationManager.markLedgerUnderreplicatedAsync(...) and immediately calls
iterCallback.processResult(OK, ...) without awaiting it. So the placementPolicyCheck latch, the
NUM_LEDGERS_NOT_ADHERING_TO_PLACEMENT_POLICY gauge and the PLACEMENT_POLICY_CHECK_TIME success
count — the only signals the test waits on — are all recorded while the ZooKeeper write creating
/ledgers/underreplication/ledgers/0000/0000/0000/0000/urL0000000000 may still be in flight. The test
then read that znode with a bare zk.exists(...).

In the failing run the mark was issued at 07:16:30,762 and the assertion ran ~490ms later, on an
attempt where the one-ledger check alone reported durationMs=409 amid ZK session churn. The test
report contains no delete of that znode and no "mark to under replication manager failed" error, so
the write had simply not landed yet.

AuditorPlacementPolicyCheckTest.testPlacementPolicyCheckWithLedgersNotAdheringToPlacementPolicyAndMarkToUnderreplication
has the identical defect — a one-shot pollLedgerToRereplicate() after auditor.close() — so it is
fixed here too rather than left as a known twin.

2. The later awaits were running on a few hundred milliseconds of slack.

In the OnRack variant the ReplicationWorker is started before the /rack2 bookie exists, so its
first replication attempt necessarily fails and defers the ledger lock release by
lockReleaseOfFailedLedgerGracePeriod / 2^5 = 9375ms (BookKeeper's default grace period is 300000),
after which the run loop backs off for another rwRereplicateBackoffMs = 5000ms. Those delays are
spent inside the Awaitility.await() calls that follow, which use the default 10s timeout. Every local
invocation took ~11.1s and logged deferring the ledger lock release {delayMs=9375}. A second failed
attempt would defer 18750ms, which the 10s await cannot survive at all.

The fire-and-forget write is upstream BookKeeper behaviour, present on apache/bookkeeper master as
well; this PR only fixes the tests.

Modifications

• TestReplicationWorker: hoist the znode path and the ZooKeeper handle above the try, and wait for
  the underreplication mark with Awaitility inside it, while the auditor is still running — so the
  wait does not race auditor shutdown and the 1s periodic placement policy check can retry a failed
  write. The second use of the path literal now reuses the local.
• TestReplicationWorker: build the test's ReplicationWorker from a dedicated ServerConfiguration
  with lockReleaseOfFailedLedgerGracePeriod=64 and rwRereplicateBackoffMs=100, the way the other
  ReplicationWorker tests in this class already do, so the awaits are not competing with ~14s of fixed
  delay. This also stops the helper mutating (and having to restore) the shared baseConf.
• AuditorPlacementPolicyCheckTest: move the pollLedgerToRereplicate() assertion into the try block
  and poll it with Awaitility, mirroring the fix above. The assertion's argument order is corrected to
  AssertJUnit's (expected, actual).

No assertion was weakened or removed: the same znode/ledger id, the same expectations.

Verifying this change

• Make sure that the change passes the CI checks.

This change is already covered by existing tests, such as
TestReplicationWorker.testRepairedNotAdheringPlacementPolicyLedgerFragmentsOnRack,
TestReplicationWorker.testReplicationStats and
AuditorPlacementPolicyCheckTest.testPlacementPolicyCheckWithLedgersNotAdheringToPlacementPolicyAndMarkToUnderreplication.

Verified locally with a temporary invocationCount (removed before this PR): 10/10, 5/5 and 10/10
passes respectively. The deferred lock release drops from delayMs=9375 to delayMs=2, and the
flaking test from ~11.1s to ~1.9s per invocation, so the awaits now have ~9.8s of headroom instead of
~0.5s. Both full test classes pass (TestReplicationWorker 14/14, AuditorPlacementPolicyCheckTest
8/8), and ./gradlew quickCheck is clean.

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

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• Dependencies (add or upgrade a dependency)
• The public API
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• Anything that affects deployment

Documentation

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Test-only change.