Skip failed-bookie recovery tasks for ledgers with writeQuorumSize=1, and clean up historical tasks without affecting placement-policy repairs.

Add dedicated metrics and regression tests for task filtering, lock release, normal recovery retries, and cleanup failures.

Fix #4872

Motivation

BookKeeper can create ledgers with writeQuorumSize=1. Every entry in such a
ledger has only one data source. If that Bookie is permanently lost, the
Auditor currently publishes an underreplication task, and the
ReplicationWorker repeatedly tries to read a source replica that cannot
exist. The retry loop consumes worker, client, and ZooKeeper resources and
creates noisy failure logs while obscuring ledgers that can actually be
recovered.

This change intentionally does not claim to recover or reconstruct lost data.
It stops an impossible automatic recovery path and exposes a dedicated metric
so operators can alert on the skipped condition and use backups or manual
recovery when data must be restored.

Changes

• Filter failed-Bookie underreplication publication in
  AuditorTask.publishSuspectedLedgersAsync:
  • Read ledger metadata before creating the underreplication mark.
  • Skip ledgers whose metadata has writeQuorumSize == 1.
  • Keep metadata-read failures fail-open, so an unknown ledger is still
    marked for normal recovery.
  • Ignore the race where the ledger was deleted before publication.
  • Count and size only ledgers actually submitted to the underreplication
    manager.
• Add NUM_SINGLE_REPLICA_LEDGERS_SKIPPED in the Auditor scope and log the
  ledger id, quorum size, reason, and action for skipped publications.
• Add a consumer-side guard in ReplicationWorker for historical tasks that
  predate this change. After taking the task lock, a task is removed through
  markLedgerReplicated when writeQuorumSize == 1 and its replicaList is
  non-empty (the failed-Bookie task shape).
• Preserve placement-policy repair tasks: a writeQuorumSize == 1 task with
  an empty replicaList continues through the existing replication path.
• Represent SUCCESS, FAILED, and SKIPPED worker outcomes separately so
  historical cleanup is not counted as replication success or failure. Add
  NUM_SINGLE_REPLICA_UNDERREPLICATED_LEDGERS_SKIPPED for this path.
• Add unit and integration coverage for single-replica filtering, deleted
  ledgers, fail-open metadata errors, published-ledger statistics, historical
  cleanup, placement-policy task preservation, and skipped-operation metrics.

Compatibility and operational notes

No configuration, ZooKeeper schema, protobuf field, or public API is added.
The behavior is deterministic from ledger metadata and applies on upgrade.
Existing underreplication znodes are persistent, so the Worker-side guard is
required to converge historical failed-Bookie tasks. Tasks with an empty
replicaList, unreadable metadata, or a concurrent znode version change are
not forcibly removed by the single-replica cleanup guard. If metadata is
unreadable, the Worker falls back to the normal recovery path; that path may
remove the task if recovery completes successfully.

The skipped counters are operational signals, not recovery-success counters:

• auditor.NUM_SINGLE_REPLICA_LEDGERS_SKIPPED
• replication_worker.NUM_SINGLE_REPLICA_UNDERREPLICATED_LEDGERS_SKIPPED

These counters are cumulative skip events, not a deduplicated count of unique
ledger IDs. The same ledger may be counted again during a later audit or retry.

Verification

Tests run on the branch:

mvn -pl bookkeeper-server -am -DskipTests=false \
  -Dtest='AuditorBookieCheckTaskTest,TestReplicationWorker' \
  -Dsurefire.failIfNoSpecifiedTests=false test

The command passes with 25 tests: 6 Auditor tests and 19 ReplicationWorker
tests. The full BookKeeper precommit command remains appropriate before merge:
mvn clean apache-rat:check install spotbugs:check.

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