Covariant Return Types With Clone

An overriding virtual function may return a pointer to a MORE derived type than the base declares. This is called a covariant return type and is commonly used for a clone() method.

Create a polymorphic base class Animal (virtual destructor; virtual string kind() const -> "animal"; virtual Animal* clone() const returning new Animal(*this)).
Create Dog that overrides kind() -> "dog" and overrides clone() to return Dog* (a covariant return) via new Dog(*this).

The runner clones a Dog both through an Animal* and directly, printing the copy's kind each time (see Expected Output).

Do NOT write a main function.