BEIJING — In speedskating’s team pursuit, the three team members skate single file, so close together that they move as if they were one six-legged skater, pushing and gliding in perfect unison. The race hasn’t changed much through the years. But when the men’s team pursuit races begin here on Sunday, several countries will deploy a strategy that has upended conventional skating wisdom and helped the United States set a world record. Traditionally, the lead skater peels off the front of the train every lap or two and reattaches to…