[fix][test] Run makeReadEntryProbFail's errorOrNot on a caller-provided executor

[lhotari]

Motivation

ManagedLedgerTest.makeReadEntryProbFail installs a Mockito answer on
LedgerHandle.readUnconfirmedAsync that consults a caller-supplied
Supplier<ManagedLedgerException> (errorOrNot) to decide whether a read should
fail. errorOrNot was evaluated directly on the thread that calls
readUnconfirmedAsync.

When a test supplies a blocking errorOrNot, that read thread is held for the
whole duration of the block, which can stall or deadlock the test. For example,
PersistentReplicatorInflightTaskTest#testReadEntriesFailedCompletesInFlightTaskAfterReplicatorTerminated
(added in #25767) blocks in errorOrNot on a CountDownLatch until the test
releases it after terminating the replicator. Because the calling thread was
blocked, the test flow could not make progress and its
failRead.await(30, SECONDS) always timed out.

Modifications

• makeReadEntryProbFail now takes an Executor that runs errorOrNot, so each
  caller decides where it runs (composing the resulting read via thenCompose).
• OneWayReplicatorTest.testProbBKErrorWhenReplicating passes
  MoreExecutors.directExecutor() to keep read interception inline and ordered
  on the calling thread — its errorOrNot never blocks.
• The three blocking PersistentReplicatorInflightTaskTest cases pass a
  dedicated single-threaded executor (@Cleanup("shutdownNow")) so a blocking
  errorOrNot runs off the read thread while reads stay ordered.

This only touches test code; production code is unaffected.

Verifying this change

This change is covered by the existing tests that use makeReadEntryProbFail.

Verified locally:

./gradlew :pulsar-broker:test \
  --tests "org.apache.pulsar.broker.service.OneWayReplicatorTest.testProbBKErrorWhenReplicating" \
  --tests "org.apache.pulsar.broker.service.persistent.PersistentReplicatorInflightTaskTest"

• OneWayReplicatorTest.testProbBKErrorWhenReplicating: passes in ~17s.

• PersistentReplicatorInflightTaskTest: 15 tests, 0 failures, including
  testReadEntriesFailedCompletesInFlightTaskAfterReplicatorTerminated.

• Make sure that the change passes the CI checks.

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

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment