Few novelists write characters as improbably multitudinous as Paul Beatty. In The White Boy Shuffe, Gunnar Kaufman is a poet, basketball player, and messiah. In Tuff, Tuffy Foshay is a drug-slinger, competitive eater, sumo-wrestling enthusiast, and candidate for city council. In Slumberland, Ferguson ‘‘DJ Darky’’ Sowell is a sax player, jukebox sommelier, porn film composer, …