add NEWS files: Enhance subscripting with attribute-based fallback

Author: bilibili12433014

Misc/NEWS.d/next/Core_and_Builtins/subscript-attr-fallback.rst

@@ -0,0 +1,6 @@
+The subscript operator (``obj[key]``) now falls back to an attribute-based
+lookup of ``__getitem__`` when the type does not define a mapping or
+sequence slot. This lookup follows normal attribute resolution rules,
+including ``__getattribute__`` and ``__getattr__``. This allows classes
+that provide ``__getitem__`` purely as an attribute or through dynamic
+attribute handlers to support subscripting.