ATHENS — Greece’s coast guard rescued 1,743 refugees and migrants over the weekend in 57 separate search-and-rescue operations near eastern Aegean islands, while the body of a young child was found washed up on an island beach, officials said. Greek authorities also freed 34 men, women and children who allegedly had been locked up in a cramped central Athens apartment by a mostly Afghan gang of extortionists that preyed on newly arrived immigrants. Greece is the main arrival point for hundreds of thousands of refugees and economic migrants seeking a better life in wealthy European countries.