“The Hardest Part,” a new song from indie pop artist Washed Out, is all about love lost, among the most human of themes.But ironically, to illustrate the tune’s sense of longing, the musician turned to something far less flesh-and-blood: artificial intelligence. With Thursday’s release of “The Hardest Part,” Macon, Ga.-based Washed Out, whose real name is Ernest Greene, has the first collaboration between a major music artist and filmmaker on a music video using OpenAI’s Sora text-to-video te...