Once upon a time, serious actors looked down on TV. Then, in the 90s, the medium began to crackle, producing, among other things, warm, sophisticated shows about relationships, such as “My So-Called Life.” In the 2000s, cable was dominant, full of rule-breaking antihero dramas. When streaming emerged, seasons got shorter and slicker, and over time “comfort TV” became the standard. Keri Russell has been a steady presence throughout these shakeups, with a key role in each era: first, the warmheart