Gov. Andrew M. Cuomo said on Tuesday that 731 more people had died in New York State, the largest single-day increase in deaths since the crisis began. The grim tally followed two days in which the numbers appeared to have leveled off. The governor emphasized that death was a lagging indicator in the fight against the virus, and pointed to a falling rate of hospitalizations and said that the state was still projecting that the spread of the virus was plateauing.