Bob Moyer reviews a new novel that he believes is an “instant classic.” Reviewed by Robert P. Moyer THE REST OF OUR LIVES. By Ben Markovits. Simon & Schuster. 240 pages. $28. John Steinbeck, Robert Pirsig, Jack Kerouac—and Ben Markovits, all authors of classic road trip books. The first three authors are well-known, of course,…