It’s a trad, trad world. Tradwives abound not just on social media — baking up their own sourdough and homeschooling half a dozen children — but also at the bookstore, where titles about women Instagramming their supposedly traditional lives are filling up shelves. Caro Claire Burke’s novel “Yesteryear,” about a modern tradwife who wakes up to find that she’s living in 1855 — and doesn’t love it — has been the undisputed book of the summer. It’s been on the New York Times bestseller list for 15 weeks and counting, and sold more than 461,000 copies, according to Circana Bookscan.…