Support cached_property on object with __slots__

Closes #12894

modules/edocument_uncefact/edocument.py

@@ -53,7 +53,7 @@ def remove_comment(stream):
 class Invoice(Model):
     "EDocument UN/CEFACT Invoice"
     __name__ = 'edocument.uncefact.invoice'
-    __no_slots__ = True  # to work with cached_property
+    __slots__ = ('invoice',)
 
     @classmethod
     def __setup__(cls):