As far as horror films go, writer-director Ian Tuason’s debut feature “Undertone” has just about everything a genre connoisseur could ever want, all rolled into one. The movie is packed with religious iconography, scary voices, possessed objects, ancient demons with silly names, maniacal senior citizens, dubious mirrors, dark corners, creepy children’s songs, creepy children’s songs played backwards, and — most terrifying of all — podcasters. With the dust from the mid-2010s podcast boom finally settling, it was only a matter of time until the medium that has become an integral part of our daily lives got the star treatment. Podcasts have been supporting elements in horror for a minute, popping up in films like “Tusk” and 2018’s “Halloween” reboot, but they’ve yet to function as a true main character. Strange, considering the medium made true-crime and horror storytelling into a viable cottage industry. But whether you’re for or against that type of voyeuristic podcasting doesn’t matter here. Unlike other horror films, “Undertone” doesn’t make podcasters the butt of the joke or a predictable first-out kill. …