By Danilo Masoni MILAN (Reuters) -A return of fund inflows into renewable energy stocks is helping to breath new life into these companies' shares, powering their strongest quarterly rise since the sustainability boom early this decade. After two years of bearish sentiment and relentless redemptions that made the sector a short-sellers' hotspot, a fundamental shift in the U.S. power demand outlook and greater policy certainty are luring investors back. U.S. President Donald Trump's "One Big Beautiful Bi ...