“Swarm”, Donald Glover’s new Prime Video series, marks Billie Eilish’s acting debut. Swarm is a thriller about Dre (Dominique Fishback), a superfan of Ni’Jah, a Beyoncé-like pop artist, who gets deadly in her obsession.  Eilish portrays a cult leader named “Eva.” Fans loved seeing Eilish get into her acting bag.  “Billie acting era, I’m here…