Ari Aster and Yorgos Lanthimos, who helmed “The Favourite,” have each developed an unmistakable filmmaking voice. But this year, both stretched into brand-new cinematic territory. With “Beau Is Afraid,” Aster crafted a nearly three-hour fever dream chronicling the mental unraveling of its profoundly neurotic title character, played to the hilt by Joaquin Phoenix.