Refactor parameter registry cache key retrieval

- Updated the `_param_registry_cache_key` function to safely access the configuration directory, ensuring it checks for the existence of `_config_dir` before attempting to retrieve the modification time of the engine parameters catalog.
- Improved error handling by encapsulating the file modification time retrieval in a conditional check, enhancing robustness against potential OSError exceptions.

Author: lapy

backend/routes/models.py

@@ -224,12 +224,14 @@ def _param_registry_cache_key(store, engine: str) -> str:
     ) else None
     version = (active or {}).get("version") or ""
     catalog_mtime = 0.0
-    try:
-        catalog_mtime = os.path.getmtime(
-            os.path.join(store._config_dir, "engine_params_catalog.yaml")
-        )
-    except OSError:
-        pass
+    config_dir = getattr(store, "_config_dir", None)
+    if config_dir:
+        try:
+            catalog_mtime = os.path.getmtime(
+                os.path.join(config_dir, "engine_params_catalog.yaml")
+            )
+        except OSError:
+            pass
     return f"{engine}:{version}:{catalog_mtime}"