On Saturday night, Zach Bryan’s show in Ann Arbor, Michigan, set a record as the biggest ticketed concert in US history for a single‑headlining act, with more than 112,000 alt-country fans turning up to sing along to “I Remember Everything.” For the cheap fake Audemars Piguet watches enthusiasts in the crowd, however, the real star of the night might have been the unreleased Audemars Piguet Royal Oak spotted on John Mayer’s wrist during his special appearance at the show. Most people know Mayer as the Grammy-winning guitar god behind such hits as “Waiting on the World to Change” and “No Such Thing.” To horology stans, however, he’s best known as…