Long-term statistics for battery-related sensors

[0.1.5] - 2026-03-01

Added

• Added long-term statistics support for battery-related sensors.
• Battery voltage and battery percentage sensors are now marked as measurement
  sensors, enabling Home Assistant long-term statistics and historical trends.
• Added battery_percent_rechargeable sensor to provide a more realistic battery
  level estimation when using rechargeable batteries (e.g. NiMH).

Changed

• Improved battery sensor metadata to align with Home Assistant best practices
  for long-term statistics (state class and measurement semantics).
• Clarified separation between vendor-style battery percentage and
  rechargeable battery estimation.