The TMDBClient was being instantiated but never closed, causing 'Unclosed
client session' errors in the logs. Fixed by using 'async with' context
manager which properly calls close() on exit.
Changes:
- _lookup_tmdb_id_by_name: wrapped client in async with
- _fetch_tmdb_data: wrapped client in async with
- Call _load_series_into_memory() before NFO scan phases to sync DB
to SeriesApp memory, fixing missing NFO for recently resolved folders
- Add TMDB lookup for series without cached tmdb_id during NFO creation
- Add get_tmdb_client() factory and get_tmdb_image_base_url() helpers
- Fix: use get_tv_show_details instead of deprecated get_series_details
- Fix tests: mock _load_series_into_memory in NFO scan tests
- Add nfo_scan_after_rescan config option (default: true)
- Implement year caching in AniworldLoader and EnhancedAniWorldLoader
- Make get_year abstract method in base provider
- Run NFO validation/creation after scheduled rescan completes
- Add _YearDict cache to avoid re-extracting year from HTML
