Robert Downey Jr. and Mark Ruffalo first met 28 years ago, through their girlfriends at the time, before hunting a serial killer in David Fincher’s “Zodiac,” and well before battling Thanos in Marvel’s “Avengers” movies. The milage on their friendship shows in their shared enthusiasm for their electrifying performances this year: Downey in Christopher Nolan’s “Oppenheimer” as the calculating U.S. Atomic Energy Commission official Lewis Strauss, and Ruffalo in Yorgos Lanthimos’ “Poor Things” as Duncan Wedderburn, an unscrupulous libertine. Both actors stretched far beyond their well-established movie star personas, and they were eager to ask each other about how they’d done it. Robert Downey Jr.: We really met when Fincher cast us in “Zodiac.” Mark Ruffalo: What a wild ride that was.