Michael Schneider Variety Editor at LargeNicholas Britell has become one of the most in-demand film and TV composers in recent years, thanks to his work on “The Big Short,” “Moonlight” and “If Beale Street Could Talk.” But it’s “Succession,” including that catchy instrumental theme song, which Pusha T made into a stunning rap, that has been unlike anything else in his career.That became apparent late last summer, as Season 2 of the HBO drama turned into a phenomenon, right when the cast and