(Reuters) -British opioid addiction treatment maker Indivior Plc said on Wednesday it was exploring a secondary listing in the United States, its biggest market, after posting a rise in annual sales buoyed by its newer injectable therapy. The London-listed company has been focusing on growing newer treatments, including the injectable Sublocade, and has benefited from patients resuming routine visits to clinics and hospitals where most of its treatments have to be administered. The growth is a boost for Indivior, which in recent years was grappling with competition and drawn-out legal challeng…