SPOILER ALERT : This post contains spoilers for Episode 3 of “ The Lady ,” available now on Britbox in the U.S. Based on the way Mia McKenna-Bruce and Ed Speleers’ characters first meet in the second episode of “The Lady,” one would think the series is a rom-com. Filming on the swanky lower level of steakhouse Smith & Wollensky on a sunny day in London last May, the two actors spent several takes making sure they got the moment just right. It’s 1998, and Jane Andrews (McKenna-Bruce) — who has