The Canadian dance-pop experimenter Jessy Lanza makes fun, frothy, futuristic music, but its upbeat textures can conceal some serious emotional depths. That’s the case for Lanza’s new song “Slapped By My Life,” which she wrote for her husband and collaborator Winston Case when Case was undergoing cancer treatments. Over shimmery keyboards and rat-tat-tat gun programming, Lanza wistfully chants, “I’m gonna …