Explicitely log a warning when the helper doesn't support cache

Closes #278 (closed)

arkindex_worker/cache.py

@@ -378,11 +378,13 @@ def merge_parents_cache(paths: list, current_database: Path):
 
 def unsupported_cache(func):
     def wrapper(self, *args, **kwargs):
+        results = func(self, *args, **kwargs)
+
         if not self.is_read_only and not self.use_cache:
             logger.warning(
                 f"This API helper `{func.__name__}` did not update the cache database"
             )
 
-        return func(self, *args, **kwargs)
+        return results
 
     return wrapper