Add max_time/min_time to statistics data

[ciux23]

Describe your core improvement

Propose extending the recorder.get_statistics API to expose timestamps of extreme values by adding:

Add max_time and min_time outputs to recorder.get_statistics to show EXACTLY WHEN extreme values occurred.

Current limitations

• Currently only get numerical max/min values
• No way to know if temperature peaked at 14:00 or 20:00
• Forces users to write complex database queries
• Missing critical timing data for automations

Technical benefits

✅ Zero breaking changes - Only adds new fields
✅ No performance impact - Uses existing timestamps
✅ Standard implementation - Matches how other systems work
✅ Immediately useful - Solves real analysis problems

Additional context

Example use cases:

• ⏱️ See WHEN your solar production peaked today
• 🔥 Find out what TIME your house was hottest
• 💡 Track exactly WHEN lights turn on/off

Technical proof:
The data ALREADY EXISTS in the statistics table (timestamp column), we just need to expose it.

How others do it:

-- Standard SQL approach
SELECT 
  MAX(value) as max_value,
  (SELECT timestamp FROM statistics WHERE value = MAX(s.value) LIMIT 1) as max_time
FROM statistics s

Mock response:

{
  "statistic_id": "sensor.temperature",
  "max": 30.5,
  "min": 18.2,
  "max_time": "2025-06-28T14:30:00+02:00",
  "min_time": "2025-06-28T05:15:00+02:00"
}