WIP: Redis Cluster / TLS support

[sriram1900]

Description

Work in progress for Redis Cluster / TLS support.

Related issue

Fixes #40

Changes

• Added tests covering the existing RedisCache client-construction behavior.
• Verified the Redis cache tests pass.
• Next: implement Redis Cluster client selection and TLS configuration.
• Documentation will be updated after implementation.

This PR is currently a draft and is not ready for final review.

[codeforstartups]

Thanks for starting on this @sriram1900! Holding off on merge since it's marked WIP — a couple of notes to move it forward:

1. Scope vs title — the PR is titled Redis Cluster / TLS support (Redis Cluster / TLS support #40), but the diff currently only adds two unit tests for existing RedisCache URL/client construction. To close Redis Cluster / TLS support #40 we'd want the actual feature: RedisCluster support and TLS (rediss:// / ssl=True + cert options) in src/dynavec/cache.py, with these tests covering the new paths.
2. Formatting — there are missing blank lines between the new test functions (e.g. test_redis_cache_uses_url_to_create_client runs straight after the previous function, and before test_redis_cache_stats). That'll trip ruff (E302) in CI — please run make format / ruff check --fix.
3. Once it's ready, flip it out of draft and I'll re-review. The two tests themselves look like a reasonable start on the injection/URL behavior. 👍