[good first issue] Testcontainers Redis Cluster IT (prove hash-tag slot co-location)

[DavidHLP]

Goal

Validate that Redisson distributed-lock keys are hash-tag-pinned to the same Cluster slot as their cache key (WS-1.2b) under a real Redis Cluster topology (not just key-construction-level).

Scope (v0.2.0, P1)

• Extend AbstractRedisIntegrationTest with a redis-cluster Testcontainers fixture (or a new AbstractRedisClusterIntegrationTest).
• One test: PUT a key under sync=true, assert the lock key co-locates on the same node (no CROSSSLOT error under Cluster).

Acceptance

• IT passes against a real cluster container (redis:7 cluster mode).
• No CROSSSLOT errors.

Refs

• COMPATIBILITY.md (Known limitations), guide §v0.2.0, wiki/architecture/cache-lifecycle.md