Add comprehensive tests for timezone functionality: - Init (valid/invalid timezones, default) - getUTCOffset - Now (with/without location) - Location (with/without location) - Name (with/without name) - StartOfDay, Today, EndOfDay - StartOfWeek (Monday-based) - StartOfMonth - ParseInLocation - ParseInUserLocation (valid/empty/invalid TZ) - NowInUserLocation - StartOfDayInUserLocation Coverage: timezone 45.2% → 93.5%