fix: eliminate Redis TOCTOU race on step cache ops

[VedantMadane]

Summary

Fixes a classic TOCTOU race between Redis null-checks and later hgetall/hset/expire calls (#71).

Holding a getRedis() reference across await boundaries is unsafe: resetRedis() (e.g. test teardown) or a mid-run disconnect can leave a dangling client that throws and crashes step execution.

Changes

• Add non-throwing helpers in src/redis.ts: redisHGetAll, redisHSet, redisExpire
  • Re-resolve the client at call time (no long-lived reference)
  • Catch connection/command errors and degrade (empty cache / skip write) instead of throwing
• Use helpers from runSteps step-cache paths and from data-cache global/project Redis ops
• resetRedis() now nulls the module reference before disconnect()
• Unit tests for success, failure, unconfigured, and mid-flight reset paths
• CHANGELOG.md entry under [Unreleased] / Fixed

Test plan

• pnpm run build (tsc clean)
• vitest: redis.test.ts, data-cache.test.ts, integration/run-steps.test.ts (36 passed)

Fixes #71

Signed-off-by: Vedant Madane 6527493+VedantMadane@users.noreply.github.com