Sometime Sunday in a game against the Los Angeles Rams, Trey Lance will take his first snap in a competitive game as a Cowboys quarterback. In fact, he hasn’t played a down since last August, back when he was with the 49ers. He wasn’t thinking that he’d be moving to the Cowboys. Rather, he was lined up behind Brock Purdy, hoping to get his old starting job back. Then the 49ers, surprisingly, dealt Lance to Dallas for a fourth-round pick. It was too late in the preseason for the former No. 3 pick of the 2021 NFL Draft to see any action. Then he didn’t play at all last fall. These days, he’s com…