The long sheds at North America's largest bitcoin mine look endless in the Texas sun, packed with the type of machines that have helped the United States to become the new global hub for the digital currency. The operation in the quiet town of Rockdale is part of an already bustling U.S. business now further boosted by Beijing's intensified crypto crackdown that has pushed the industry west. Experts say rule of law and cheap electricity in the United States are a draw for bitcoin miners, whose energy-gulping computers race to unlock units of the currency. "There's a lot of competitors…