Play Framework

feat: bind Hibernate + JCache (L2) metrics to Micrometer (PF-86 follow-up)

Extends PF-86's cache observability beyond the framework's CaffeineImpl
to cover the Hibernate side of the stack:

* HibernateMetrics.monitor() — bound per SessionFactory at JPAPlugin
  startup, tagged with db=<dbName>. Emits hibernate.connections.obtained,
  hibernate.transactions, hibernate.flushes, hibernate.cache.requests
  (with result=hit|miss, region=<region> tags), and the dedicated
  hibernate.second.level.cache.* series.
* JCacheMetrics.monitor() — iterates the default JSR-107 CacheManager
  and binds each cache, picking up Hibernate L2 regions when L2 is
  configured with hibernate.cache.region.factory_class=
  org.hibernate.cache.jcache.JCacheRegionFactory. Apps without L2
  trigger CachingProvider not-found which is demoted to debug-level.
* hibernate.generate_statistics defaulted to true (via putIfAbsent so
  app overrides win). HibernateMetrics produces zeros without it.

The HibernateMetrics call goes through reflection deliberately:
Micrometer 1.13.x..1.16.x ships the binder with overloads referencing
both org.hibernate.SessionFactory and the legacy
javax.persistence.EntityManagerFactory. Java's overload resolution
loads every overload's parameter types up front, so a direct call
fails to compile on this jakarta-only classpath. Reflection names the
SessionFactory overload only and dodges the issue without polluting
the dependency graph with javax.persistence-api just to satisfy javac.

Cache surface audit summary: framework caches now bound — Caffeine
(PF-86), Hibernate aggregate (this commit), Hibernate L2 / JCache
(this commit), HikariCP pool (PF-85). MemcachedImpl is uncovered
because spymemcached has no Micrometer binder upstream; that's an
alternative cache backend used by a minority of deployments.
Internal LRU caches (BytecodeCache, classDefsInFileCache,
staticPathsCache) are intentionally skipped — low-value internal
state, not user-facing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>