The cost of hiring a supertanker from the Middle East to China exceeded $200,000 a day on Thursday for the first time since 2020 as the threat of U.S. attacks on Iran grows and buyers seek to lock in oil cargoes, according to data and market sources.Iran pledged to show flexibility at indirect talks with Washington on their longstanding nuclear dispute on Thursday, with Tehran under pressure to agree to a deal or face U.S. military strikes. The Strait of Hormuz runs along Iran's…