Potential fix for pull request finding 'Empty except'

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

Author: ChenZiHong-Gavin

graphgen/models/storage/rocksdb_cache.py

@@ -21,6 +21,7 @@ def delete(self, key: str):
         try:
             del self.db[key]
         except KeyError:
+            # If the key does not exist, do nothing (deletion is idempotent for caches)
             pass
 
     def close(self):