fix: gate public cache inside cache impl

[OXeu]

Summary

• move the public cache toggle into CacheImpl itself instead of relying on an outer wrapper
• ensure only the public cache store is gated by cache.enabled, while config stores remain readable to avoid recursion
• keep the existing cache setting semantics and add a regression test covering the non-recursive config path

Testing

• cd server && bun run check
• cd server && bun test ./src/utils/tests/cache.test.ts ./src/services/tests/feed.test.ts ./src/services/tests/moments.test.ts

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