HBASE-30025 Wire TieredExclusiveTopology as a CombinedBlockCache-compatible CacheAccessService

[VladRodionov]

Summary

This PR adds a construction path for creating a topology-backed CacheAccessService
from existing L1 and L2 BlockCache instances.

The pluggable block cache architecture now has the basic components needed for
topology-backed cache access:

• CacheEngine
• CacheTopology
• CachePlacementAdmissionPolicy
• CacheAccessService
• TieredExclusiveTopology
• TopologyBackedCacheAccessService
• BlockCacheBackedCacheEngine

This PR wires those pieces together for the current CombinedBlockCache-style L1/L2
model. Existing BlockCache instances are adapted to CacheEngine using
BlockCacheBackedCacheEngine, assembled into a TieredExclusiveTopology, and exposed
through TopologyBackedCacheAccessService.

Changes

• Adds TopologyBackedCacheAccessServices, a small helper class for constructing
  topology-backed cache access services.
• Adds fromTieredExclusiveBlockCaches(...) for creating a
  TopologyBackedCacheAccessService from existing L1 and L2 BlockCache instances.
• Adds tests verifying that the constructed service uses:
  • BlockCacheBackedCacheEngine for L1 and L2 adaptation
  • TieredExclusiveTopology
  • the supplied CachePlacementAdmissionPolicy
• Adds behavior tests for CombinedBlockCache-compatible exclusive tier behavior:
  • L1 hit
  • L2 hit
  • miss
  • L2-to-L1 promotion
  • rejected cache insertion
  • cache insertion into policy-selected tiers
  • eviction from both tiers
  • shutdown propagation

Why this is needed

The current production L1/L2 block cache model is represented by CombinedBlockCache,
typically coordinating LruBlockCache as L1 and BucketCache as L2.

The new architecture models this as:

CacheAccessService
  -> CacheTopology
      -> CacheEngine(s)

AI assistance disclosure

This PR was prepared with assistance from ChatGPT. All changes were reviewed, tested,
and submitted by the author.