The sprawling Wind Technology Testing Center in Charlestown, built with state and federal dollars at a cost of about $40 million, aims to help the wind industry develop turbines better able to survive gale-force winds, blizzards, and other tests of nature. It’s the first facility in the nation where manufacturers can put their technology through the motions, and state officials and contractors said the year-old center is allowing manufacturers to build larger, more powerful, and cost-effective turbines.