Fixed issue #60 where Tibber API temporarily returning incomplete data
(None values during maintenance) caused AttributeError crashes.
Root cause: `.get(key, default)` returns None when key exists with None value,
causing chained `.get()` calls to crash (None.get() → AttributeError).
Changes:
- api/helpers.py: Use `or {}` pattern in flatten_price_info() to handle
None values (priceInfo, priceInfoRange, today, tomorrow)
- entity.py: Use `or {}` pattern in _get_fallback_device_info() for address dict
- coordinator/data_fetching.py: Add _validate_user_data() method (67 lines)
to reject incomplete API responses before caching
- coordinator/data_fetching.py: Modify _get_currency_for_home() to raise
exceptions instead of silent EUR fallback
- coordinator/data_fetching.py: Add home_id parameter to constructor
- coordinator/core.py: Pass home_id to TibberPricesDataFetcher
- tests/test_user_data_validation.py: Add 12 test cases for validation logic
Architecture improvement: Instead of defensive coding with fallbacks,
implement validation to reject incomplete data upfront. This prevents
caching temporary API errors and ensures currency is always known
(critical for price calculations).
Impact: Integration now handles API maintenance periods gracefully without
crashes. No silent EUR fallbacks - raises exceptions if currency unavailable,
ensuring data integrity. Users see clear errors instead of wrong calculations.
Fixes#60
