Netflix's next great binge-worthy show has arrived, and it's a brash, bracing headfuck with just the right amount of heart. Russian Doll, the propulsive new series from Natasha Lyonne, Amy Poehler, and Leslye Headland, is a brilliant tale of morality and mortality that finds an expert balance between sincerity, cutting comedy, and wild genre flourish. In the first episode, we meet Nadia (Lyonne); an acerbic, chain-smoking software designer in rockstar duds, staring herself down in the bathroom mirror at her 36th birthday party. Outside the walls of the wildly designed bathroom (including a "terrifying" door that …