It’s been almost exactly a decade since “ Nashville ” left ABC. Though the show continued for two more seasons on CMT, its main period of acclaim and attention — between 2012 and 2016 — was guided in large part by Hayden Panettiere . Panettiere’s character, the rising country-pop star Juliette Barnes, became the show’s center of gravity in its first several seasons. But what no one knew at the time was the toll the series was taking on one of its stars. The filming of “Nashville” is just one of