fix(api): correct path retrieval in scan_extensions method

The previous does not work when `cwd` is not `api`, switching to
`__file__` fixes this.

api/core/extension/extensible.py

@@ -42,7 +42,7 @@ class Extensible:
         position_map: dict[str, int] = {}
 
         # get the path of the current class
-        current_path = os.path.abspath(cls.__module__.replace(".", os.path.sep) + ".py")
+        current_path = os.path.abspath(__file__)
         current_dir_path = os.path.dirname(current_path)
 
         # traverse subdirectories