WASHINGTON — President Obama made a vigorous appeal to Congress on Thursday to give breathing space to his efforts to forge a nuclear deal with Iran, and the prospects for an interim agreement may have improved with the release of a report by international inspectors who said that for the first time in years, they saw evidence that the Iranians have put the brakes on their nuclear expansion. The inspectors, from the International Atomic Energy Agency, said that very few new advanced centrifuges had been installed since President Hassan Rouhani of Iran took office in June, promising a new start with the West, and that little significant progress has been made on the construction of a new nuclear reactor, which became a point of contention in negotiations in Geneva last week. The slowdown, according to diplomats familiar with the Iranian work, was clearly political, not driven by technical problems. […]