Aaron Paul has joined the cast of “ Fallout ” Season 3. Details about his role are kept under wraps, while Annabel O’Hagan and Dave Register have been promoted to series regulars on the Amazon Prime Video sci-fi drama. The casting marks a reunion between Paul and executive producers Jonathan Nolan and Lisa Joy, who cast the “Breaking Bad” star in the final season of their show “Westworld.” Created by Graham Wagner and Geneva Robertson-Dworet, “Fallout” is based on the post-apocalyptic video game franchise of the same name. It stars Ella Purnell, Aaron Moten, Kyle MacLachlan, Moisés Arias, Xelia Mendes-Jones, Walton Goggins and Frances Turner. Popular on Variety “Fallout” takes place 200 years after a nuclear holocaust, when sheltered vault dwellers are forced to return to the violent and bizarre wasteland their ancestors left behind. The first two seasons of the series rank among the most-watched seasons of television on Amazon Prime Video.…