A year out from the first season finale of “The Flight Attendant,” Cassie Bowden is newly sober, settled down in Los Angeles and on the payroll of the CIA. And for just a brief second, it seems like this all could be working. But the joy of the show, returning to HBO Max Thursday, is watching Cassie, played by Kaley Cuoco, spiral. “A big conversation that we had right off the bat was ‘well, she isn’t drunk anymore, so we don’t get to have the same fun,’” showrunner Steve Yockey told the Daily News. “But we do, because the alcohol was just masking the underlying issues. She’s still addicted to …