In “Heartburn,” Meryl Streep (Rachel) and Jack Nicholson (Mark) eat spaghetti carbonara in bed and they’re headed for a breakup. In “Bridget Jones’s Diary,” Renee Zellweger (Bridget) snuggles under the covers for a rendezvous with excessive amounts of comfort food. Neither is a formula for a good night’s sleep. But there are foods that can improve your sleep, just don’t eat them in bed, or too clo…