“She-Hulk: Attorney at Law,” which just debuted on Disney+, is arguably the most delightful Marvel Studios series yet. Created by Jessica Gao and starring Tatiana Maslany as the lawyer-turned-superhero, “She-Hulk” is effervescent and refreshing, a balmy tonic after the darkness of “Doctor Strange in the Multiverse of Madness” and other, more somber Marvel Studios productions.