By Stephanie Apstein Four years after a disastrous performance cost him a chance at Olympic glory, the 22-year-old dominated in Beijing on Tuesday. To win, he must continue to fight off nerves—and a positive test. BEIJING — After it was over, after he had scored a world-record-shattering 113.97 points to take a commanding lead in the men’s figure skating event on Tuesday, after he had erased the disappointment of a disastrous 2018 performance, after he released a weight he has carried for nearly 20% of his life, Nathan Chen thought about what had just happened. Did he really do that? Not the s…