feat(feature-flags): generalize driver-side cache

[cathleeny]

Summary

• Move the existing feature-flag cache into driver scope and cache all returned flag values.
• Add typed getters for Boolean, int32, int64, double, string, and string list; use BigInt for exact int64 values.
• Share values by workspace ID, with normalized host as a fallback, while keeping authentication and transport caller-owned.
• Route telemetry through getBoolean and release cache references on reconnect/close.

The cache can be used after driver authentication is configured, before a backend/session is opened. This does not add a kernel-selection flag, an automatic pre-kernel GET, or a kernel version bump.

Validation

• 1,350 unit tests passing.
• Driver build passed.
• ESLint and Prettier checks passed for the updated cache.
• Covers typed values, workspace sharing, TTL refresh/failure behavior, and reconnect/close cleanup.

[cathleeny]

Replaced by #543, a direct upstream draft with identical commits. Closing this fork-based draft.