HBASE-30380 Add configuration change propagation through CacheAccessService

[VladRodionov]

Summary

Propagates runtime configuration changes through the CacheAccessService / CacheEngine
architecture instead of relying on the legacy BlockCache compatibility reference.

Changes

• Make CacheEngine participate in HBase configuration updates via
  ConfigurationObserver, with a default no-op onConfigurationChange(Configuration).
• Add a default no-op configuration callback to CacheAccessService.
• Implement configuration propagation in TopologyBackedCacheAccessService.
• Forward configuration changes to every CacheEngine participating in the active
  CacheTopology.
• Update CacheConfig.registerChildren() and deregisterChildren() to register the
  CacheAccessService rather than the legacy BlockCache.
• Preserve legacy BlockCache configuration behavior through BlockCacheBackedCacheEngine.
• Add tests for configuration propagation through single-tier and tiered topologies and
  CacheConfig child registration.

Motivation

CacheAccessService is now the primary cache abstraction and can be backed by native
CacheEngine implementations which do not expose a legacy BlockCache.

Registering only the legacy BlockCache with the configuration propagation mechanism would
therefore bypass native cache engines.

This change makes CacheAccessService the configuration propagation root for the cache
subsystem:

CacheConfig
    |
    v
CacheAccessService
    |
    v
CacheTopology
    |
    +--> CacheEngine
    +--> CacheEngine

Legacy BlockCache implementations continue to receive configuration updates through
BlockCacheBackedCacheEngine, avoiding duplicate registration and keeping the migration
path compatible with existing cache implementations.