Photo: Michael Nagle/Bloomberg/Getty Images Zohran Mamdani , a quick learner, has joined a long list of New York mayors who took the oath of office and promptly began slamming their predecessor for leaving the city’s finances in shambles. At the White House, in a tradition started by Ronald Reagan, departing presidents have left a personal handwritten note on the Resolute Desk for their successor to discover upon entering the Oval Office after the inauguration. Here in Gotham, newly minted