A&E’s “Nightwatch Nation” shines a light on the after-dark world of EMTs and paramedics in Yonkers. The series, premiering Thursday at 10 p.m., follows three crews from Empress Ambulance, a Yonkers EMT service, as they work the overnight shift. It’s a spinoff of A&E’s “Nightwatch,” which tracked not only EMTs but fire departments and police...