Migration: Use TimeTravel in Unit Tests

[bolshakov]

What changed:

• All unit tests updated to use TimeTravel for metrics snapshots, state transitions, recovery timing
• All assertions on timestamped values now use frozen time
• Tests run 100% deterministically regardless of system clock

Part of: 3-phase refactoring (Phase 2/3)

• Depends on: Redis-Synchronized Time: Infrastructure & TimeTravel Helper #917 (infrastructure)
• Enables: Production Code: Use Redis Time in State & Metrics #920 (production code to use now())

[github-actions]

Review price tag

🟢 36 effective lines — about 5–11 min (down from 44–111 min) of focused review (based on 200–500 lines/hour). This is within the range where reviewers find the most issues per line, and small changes usually receive feedback the fastest.

Spread across many files. This PR changes 10 files — more than about 9 in 10 PRs touch. Each extra file is another piece of context a reviewer has to load and hold at once.

Why these numbers?

These minutes are what careful defect-finding costs at 200–500 lines/hour — the rate review studies report, not how long a skim takes. "Effective lines" already exclude generated files and lockfiles. Treat the rates and the 200/400 thresholds as guardrails, not laws.