KAFKA-10397: do not expose statistics-based RocksDB metrics when the user provides a Statistics object

[Aangbaeck]

Summary

KAFKA-10397

When a user supplies their own Statistics object to a RocksDB state store through
RocksDBConfigSetter, RocksDBStore passes null to the metrics recorder, because
Kafka Streams must not read the user's Statistics — reading it via
getAndResetTickerCount() would reset the user's counters. As a result
RocksDBMetricsRecorder.record() short-circuits and the statistics-based metrics are
never recorded. They were, however, still registered in init() and therefore exposed
as perpetually-empty metrics.

Affected (statistics-based, RecordingLevel.DEBUG) metrics: bytes-written,
bytes-read, memtable-bytes-flushed, memtable-hit-ratio,
memtable-flush-time-{avg,min,max}, write-stall-duration,
block-cache-{data,index,filter}-hit-ratio, bytes-{read,written}-compaction,
compaction-time-{avg,min,max}, number-open-files, number-file-errors.

Fix

Register the statistics-based sensors lazily in addValueProviders(), only once a value
provider with a non-null Statistics is added, instead of unconditionally in init().
The property / block-cache gauges read the RocksDB instance directly and remain valid
without a Statistics object, so they are still registered in init() as before.
record() additionally guards on whether the sensors were registered.

Only the user-provided-Statistics case changes; the default (Streams-owned Statistics
at RecordingLevel.DEBUG) and the property-based gauges are unchanged in all cases.

Testing

• RocksDBMetricsRecorderTest — new/updated unit tests: gauges (not sensors) are
  registered on init(); statistics-based sensors are registered when value providers
  with a Statistics are added, not registered when Statistics is absent, and
  registered only once across multiple segments.
• RocksDBStoreTest.shouldNotRegisterStatisticsBasedMetricsWhenUserProvidesStatistics —
  end-to-end: with a user-provided Statistics at DEBUG, a statistics-based metric
  (bytes-written-total) is not registered while a property gauge
  (num-entries-active-mem-table) still is.
• checkstyle, spotless and spotbugs pass.

Note on compatibility / KIP

This changes which metrics are registered in the specific case of a user-provided
Statistics object (they were always empty in that case); it does not change the
documented metric set for the default configuration. The JIRA (filed by a committer) is
not tagged needs-kip — flagging here so reviewers can confirm whether any KIP or
compatibility note is warranted.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com