PROVIDENCE, R.I. — Seven hours of federally mediated talks between Lifespan and the United Nurses and Allied Professionals Local 5098 ended Wednesday afternoon without a settlement. The parties say they will return to the bargaining table on Friday, for what will be the sixth such session of talks in a summer labor dispute that has included a three-day strike by the union and a one-day lockout by Lifespan, which runs Rhode Island and Hasbro Children’s hospitals.