Remove flushAll from DialCache and Redis adapter contracts

[lan17]

Priority

P0 — Critical — resolve before the next release presented as production-ready.

Problem

DialCache.flushAll() delegates to raw Redis/Valkey FLUSHALL, ignores redis.keyPrefix, and broadcasts across every cluster primary. A library-scoped maintenance method can therefore delete unrelated application data.

Evidence on reviewed main (2bda04d1443a75a71cbbc41365c4424554936a37):

• High-level API
• Semantic Redis interface
• node-redis cluster broadcast
• GLIDE cluster broadcast

Confirmed decision

Remove this capability entirely. Do not add a replacement clearing API in this issue.

Acceptance criteria

• Remove DialCache.flushAll().
• Remove flushAll() from DialCacheRedisClient and both bundled adapters.
• Remove dead internal flush plumbing and every library-initiated FLUSHALL/flushall call.
• Update README, package-consumer mocks, unit tests, and integration tests.
• Raw administrative flushes may remain only in isolated test-fixture setup, outside the DialCache API.
• Document the breaking change in release notes.