“In Georgia, if you get a traffic ticket and you can’t afford to pay in full up front, you are put on misdemeanor probation until the fine is paid. And in Georgia, as in at least four other states, that probation is typically managed by a for-profit company. These companies — more than 20 in Georgia alone — make tens of millions of dollars each year by tacking additional fees onto probationers’ repayment plans with the threat of jail if they fall behind.”