By Tim McLaughlin and Brendan O’Brien BOSTON (Reuters) -When Long Island, New York resident Jenn Ifer is not working indoors at her COVID-19 testing company, she’s spending 10-hour days in Times Square administering PCR tests, a task that has become harder during a heat wave smothering a broad swath of the United States and breaking temperature records. Some 100 million Americans from New York City to Las Vegas will be under heat warnings this week as temperatures rise well above 100 Fahrenheit (38 Celsius), the National Weather Service (NWS) said on Wednesday. Scientists say these types of we…