Positioning itself as a female-friendly alternative to Uber, Safr, a new Boston ride-hailing service that launched last month, faces an uphill climb to take market share from an industry leader. But with Uber’s seemingly unending stream of bad news this year, and a new report revealing that thousands of Uber and Lyft drivers in Massachusetts have failed the state’s new background checks, time seems ripe for a safety-conscious ridesharing service. “There is obviously a need