Introduced TibberPricesMidnightHandler to prevent duplicate midnight
turnover when multiple timers fire simultaneously.
Problem: Timer #1 (API poll) and Timer #2 (quarter-hour refresh) both
wake at midnight, each detecting day change and triggering cache clear.
Race condition caused duplicate turnover operations.
Solution:
- Atomic flag coordination: First timer sets flag, subsequent timers skip
- Persistent state survives HA restart (cache stores last_turnover_time)
- Day-boundary detection: Compares current.date() vs last_check.date()
- 13 comprehensive tests covering race conditions and HA restart scenarios
Architecture:
- coordinator/midnight_handler.py: 165 lines, atomic coordination logic
- coordinator/core.py: Integrated handler in coordinator initialization
- coordinator/listeners.py: Delegate midnight check to handler
Impact: Eliminates duplicate cache clears at midnight. Single atomic
turnover operation regardless of how many timers fire simultaneously.
