As thousands of moviegoers gear up for double features of Greta Gerwig’s “Barbie” and Christopher Nolan’s “Oppenheimer,” one person taking joy in the “Barbenheimer” craze is Nolan himself. Although his movie will be battling “Barbie” at the box office, Nolan recently told IGN that “it’s terrific” to have both summer tentpoles open on the same day.