Add reusable components migrated from consuming project:

- Cache: AbstractCachedRepository, CacheStampedeHelper (XFetch), MsgPackMarshaller, AdaptiveMsgPackMarshaller
- Security: MessageSignerService (HMAC-SHA256), RedisNonceStore, SignedMessageMiddleware, InvalidSignatureException
- Worker: WorkerResetSubscriber (FrankenPHP/RoadRunner stateful service reset)

Update Symfony dev deps to ^7.0 || ^8.0.
Add suggest entries for optional dependencies.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>