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

src/server/providers/base_provider.py

@@ -91,6 +91,17 @@ class Loader(ABC):
             Series title string
         """
 
+    @abstractmethod
+    def get_year(self, key: str) -> int | None:
+        """Get the release year of a series.
+
+        Args:
+            key: Unique series identifier/key
+
+        Returns:
+            Release year as integer, or None if year cannot be determined
+        """
+
     @abstractmethod
     def get_season_episode_count(self, slug: str) -> Dict[int, int]:
         """Get season and episode counts for a series.