New Workouts Watch AppTests bundle wired into the watch scheme. Extracts
the phone-to-watch cache apply/prune into a pure, session-free
WatchCacheApplier seam and makes the HR-zone bucketing a nonisolated
static, so both can be unit-tested off the main actor without a live
WatchConnectivity session.
Claude-Session: https://claude.ai/code/session_01HJDQQDA9QdP8zByg43H5v3
