By Richard Cowan WASHINGTON (Reuters) -In a potential breakthrough toward the first significant new U.S. gun law in decades, a bipartisan group of senators on Sunday announced an agreement on a framework for a firearms safety bill with enough Republican support to advance in the narrowly divided Senate. The plan, praised by President Joe Biden, includes support for state “red flag” laws keeps guns from potentially dangerous people, tougher criminal background checks for firearms buyers under 21 and a crackdown on “straw purchases” by people buying firearms for others who could not pass a backg…