Wolfgang Puck and his son, Byron Lazaroff-Puck. Stella Kalinina for BI After delivering the closing speech at his bar mitzvah, marking the spiritual journey from boy to man, Byron Lazaroff-Puck turned to America's most famous celebrity chef with a promise. "Don't worry," the 13-year-old told his father, Wolfgang Puck. "In a few years, you'll be sipping mai tais in Malibu, and I'll take over." "It was just a joke," Lazaroff-Puck, now 31, tells me. "But the very next day, he came up to me and sai