The enduring power of Sandra Bullock as a rom-com heroine is one of the greatest wonders of the world. In her latest action-comedy “The Lost City,” opposite Channing Tatum, she’s just as fresh, funny and beguiling as she was 28 years ago, in her breakout role opposite Keanu Reeves in “Speed.” The characters in “The Lost City” are searching for treasure in a remote tropical jungle, but the real marvel is in front of them all along, in the form of our beloved Sandra B. The script, by Seth Gordon, Oren Uziel, Dana Fox and co-directors Aaron and Adam Nee, is uniquely suited to Bullock’s gifts for …