Add classproperty helper utility

This is apparently a 3.9+ only addition

discord/utils.py

@@ -155,6 +155,15 @@ class CachedSlotProperty(Generic[T, T_co]):
             setattr(instance, self.name, value)
             return value
 
+class classproperty(Generic[T_co]):
+    def __init__(self, fget: Callable[[Any], T_co]) -> None:
+        self.fget = fget
+
+    def __get__(self, instance: Optional[Any], owner: Type[Any]) -> T_co:
+        return self.fget(owner)
+
+    def __set__(self, instance, value) -> None:
+        raise AttributeError('cannot set attribute')
 
 def cached_slot_property(name: str) -> Callable[[Callable[[T], T_co]], CachedSlotProperty[T, T_co]]:
     def decorator(func: Callable[[T], T_co]) -> CachedSlotProperty[T, T_co]: