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

[amomchilov]

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 #3 (comment)