The Mission: Impossible franchise just got a kick-ass new femme fatale. Guardians of the Galaxy star Pom Klementieff has joined the cast of Mission: Impossible 7 (and possibly 8, depending on how much you want to read into a hashtag) alongside returning star Tom Cruise. McQuarrie announced the casting with a tweet, saying ".@PomKlementieff. How do you spell femme fatale? #MI78", to which Klementieff replied, "Mischief: accepted." The announcement makes Klementieff the first cast member and first character hints officially announced to join Cruise's Ethan Hunt in the upcoming back-to-back sequels. Previous reports suggested that McQuarrie …