Protect against misbehaved `inherited` hooks that don't call `super`

Relying on this inherited method means we only restore .new when user-defined self.inherited hooks call super. If an abstract class defines an inherited hook without super, concrete subclasses keep the abstract .new and can't be instantiated:

class Base
  abstract!

  def self.inherited(_subclass)
    # no super
  end

  abstract def call; end
end

class Impl < Base
  def call; end
end

Impl.new # raises CannotInstantiateAbstractClassError

I wonder if we should install this as a prepended singleton hook, or otherwise wrap/chain the existing hook, and add a regression test so subclass instantiation doesn't depend on user hooks calling super.

Originally posted by @Morriar in https://github.com/Shopify/type_toolkit/pull/3#discussion_r3826337769

Start by locating the implementation of the abstract! behavior and its self.inherited hook. Reproduce the Base and Impl example from the issue, then investigate how the hook can be protected when user-defined inherited methods omit super. Add the requested regression test and verify that the concrete subclass can be instantiated.