Play Framework

feat: typed Cache contract + memcached removal (PF-88, release 1.12.39)

Replaces the 2009-era memcached-centric play.cache facade with a typed,
dependency-inverted Cache architecture loaded via Java's ServiceLoader.
Framework code now references only abstractions; concrete implementations
live in their own packages and ship via SPI.

Architecture
* play.cache (framework, abstractions only, zero compile dependency on
  Caffeine or any specific backend):
  - Cache<K, V> — typed runtime contract: getIfPresent, get-with-loader,
    put, invalidate, invalidateAll, estimatedSize, stats.
  - CacheConfig — immutable builder: expireAfterWrite, expireAfterAccess,
    maximumSize, recordStats.
  - CacheStats — record (hitCount, missCount, loadCount, evictionCount,
    hitRate).
  - CacheProvider — SPI: name, create(name, config), bindMetricsToRegistry,
    stop. Default bindMetricsToRegistry is no-op for providers without
    per-cache metrics.
  - Caches — public registry: ServiceLoader resolution at boot, named()
    is computeIfAbsent per name, installProvider() for tests, lifecycle
    init/stop, invalidateAll for dev-mode hot reload.
* play.cache.caffeine (separate package, ships with the framework):
  - CaffeineCacheProvider implements CacheProvider, name="caffeine".
  - CaffeineCache<K, V> wraps com.github.benmanes.caffeine.cache.Cache.
  - META-INF/services/play.cache.CacheProvider registers via SPI.

Provider selection (Caches.selectProvider, package-private for test):
* Zero providers → ConfigurationException at boot.
* One provider → use it.
* Multiple → require cache.provider=<name> in application.conf; mismatch
  fails fast with diagnostic listing all registered names.

Re-implemented user-surface features on the new contract
* @CacheFor — ActionInvoker.actionCache(ttl) → Caches.named("play.actions."
  + ttl, CacheConfig with matching expireAfterWrite). One backing cache
  per distinct TTL string so each cache's expireAfterWrite matches the
  declared duration (Caffeine eviction is per-cache, not per-entry). Drop
  the Serializable constraint inherited from memcached. Annotation
  surface unchanged.
* #{cache for:'10m'} — FastTags.fragmentCache(ttl) → Caches.named(
  "play.fragments." + ttl, ...). Same pattern. Tag surface unchanged.

Deletions
* play.cache.MemcachedImpl (entire ~270-line class).
* play.cache.CaffeineImpl (replaced by CaffeineCache + Provider).
* play.cache.CacheImpl (replaced by CacheProvider returning typed Cache).
* play.cache.Cache static facade (set/get/add/replace/incr/decr/safe*/
  Object overloads — all gone). Hard break per ticket; no compatibility
  shim.
* play.cache.checkSerializable.
* spymemcached-2.12.3.jar from framework/lib.
* net.spy -> spymemcached entry from framework/dependencies.yml.
* memcached=/memcached.host= keys from application-skel application.conf.
* testrunner /@tests/cache HTTP debug action (only legacy facade
  consumer outside the framework itself).
* Old CacheTest + CaffeineImplTest (replaced by new typed-contract tests).

Migrated framework consumers
* Play.start/stop — Cache.init/stop → Caches.init/stop.
* ApplicationClassloader hot-reload — Cache.clear → Caches.invalidateAll.
* MetricsPlugin — bindFrameworkCacheMetrics → bindCacheMetrics; dispatches
  to provider.bindMetricsToRegistry so cache binding is now provider-
  agnostic at the plugin layer. CaffeineCacheProvider attaches Micrometer's
  CaffeineCacheMetrics for every created cache, tagged with the registered
  name.

New tests
* CachesTest — registry idempotency (named returns same instance per
  name), invalidateAll, named-before-init fails loudly, installProvider
  stops the previous provider.
* CachesProviderResolutionTest — drives selectProvider directly with
  fabricated candidate lists: zero / single / multiple-without-config /
  multiple-with-matching-config / multiple-with-mismatched-config.
* CaffeineCacheTest — putAndGetIfPresent, get-with-loader (loader runs
  once on miss), expireAfterWrite TTL, maximumSize bounds (with
  cleanUp() to drain Caffeine's async maintenance), recordStats hit/miss/
  load tracking, zero-stats snapshot when recording disabled,
  bindMetricsToRegistry attaches every created cache.

Docs
* documentation/manual/cache.textile — rewritten end-to-end on the new
  API. Documents Caches.named, CacheConfig, the SPI extension point for
  alternate backends, the test-override path, and the migrated @CacheFor
  / #{cache} surfaces.
* documentation/manual/configuration.textile — memcached section
  replaced with cache.provider config key + cross-link to the cache page.
* documentation/manual/releases/release1.12.x/releasenotes-1.12.0.textile
  — adds h4 1.12.39 PF-88 subsection summarizing the contract change,
  what's deleted, and the SPI extension story.

Build
* framework/build.xml — copy fileset extended to include
  META-INF/services/** so the SPI registration ships in the jar.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>