Act I of “Turandot,” directed by Andrei Şerban, Washington National Opera, 2009 (photo by Karin Cooper) After a spring season of more challenging operas — a vicious Peter Grimes and a controversial, Americanized Siegfried — Washington National Opera brought home the bacon on Saturday night, opening its final production, Puccini’s Turandot. The company presented this opera last time only in 2001 (with Alessandra Marc in the title role), and the Kirov Opera brought its…