WASHINGTON — The United States directly purchased Argentine pesos on Thursday and finalized a $20 billion currency swap line with Argentina’s central bank, Treasury Secretary Scott Bessent said in a social media post, a rare move aimed at stabilizing turbulent financial markets in the cash-strapped Latin American ally. “U.S. Treasury is prepared, immediately, to take whatever exceptional measures are warranted to provide stability to markets,” Bessent said, adding that the Treasury Department