Fix: https://github.com/rails/rails/issues/53606



`class_attribute` never composed well with `prepend` or `alias_method_chain`.
Up to 7.2, whenever the value was re-assigned, the reder method was redefined.

Now, since 8.0, we no longer redefine the reader, or at least in less cases,
but then the writer is sometimes redefined too, which restrict even more
how much decoration can be done.

A solution to this is to define class attributes under a namespaces
and then define a two simple delegator methods to allow decoration.

Of course it's one extra method call, but that's still miles better
than what it used to be, and probably acceptable.

Co-Authored-By: zvkemp <zvkemp@gmail.com>