Fix HomeAssistant forecast cache validation to check specific future hours

[Copilot]

Cache validation incorrectly used len(cache) < hours to trigger refresh. Since cache keys are weekday_hour (e.g., "0_14" for Monday 14:00), old entries for different time slots don't satisfy forecast requirements.

Changes

• Cache validation: Check if specific required cache keys exist for forecast hours, not total cache size
• Race condition fix: Calculate now inside cache lock to avoid edge cases around hour boundaries
• Test coverage: Added test verifying stale cache entries trigger refresh when required future hours are missing

Before/After

# Before: total cache size check (incorrect)
if cache_size == 0 or cache_size < hours:
    self.refresh_data_with_limit(hours)

# After: check specific required keys
with self._cache_lock:
    now = datetime.datetime.now(tz=self.timezone)
    for h in range(hours):
        future_time = now + datetime.timedelta(hours=h)
        cache_key = self._get_cache_key(future_time.weekday(), future_time.hour)
        if cache_key not in self.consumption_cache:
            missing_keys = True
            break

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Homassistant forecast caching issues</issue_title>
<issue_description>https://github.com/muexxl/batcontrol/blob/main/src/batcontrol/forecastconsumption/forecast_homeassistant.py#L730

This line is not correct.
The length of the cache does not reflect the forecast amount in the future as older entries can be existing.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Homassistant forecast caching issues #231

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