feat: add NFO scan after rescan and year caching

- 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

tests/unit/test_base_provider.py

@@ -103,6 +103,9 @@ class ConcreteLoader(Loader):
     def get_title(self, key: str) -> str:
         return f"Title for {key}"
 
+    def get_year(self, key: str) -> int | None:
+        return 2024
+
     def get_season_episode_count(self, slug: str) -> Dict[int, int]:
         return {1: 12, 2: 24}