Iran’s discussions with the United Nations’ atomic agency about its past nuclear work have effectively stalled, with no progress expected before a Nov. 24 deadline for a broad nuclear agreement, the agency said Friday. The lack of progress will spark concerns about Iran’s determination to reach a nuclear deal. Tehran had promised real cooperation with the International Atomic Energy Agency a year ago but has barely answered any of the key questions about its past work that many western capitals believe was part of nuclear weapons research.