In “Black Flies” the full-frontal reality of two nighttime paramedics grabs you at the throat and doesn’t let go. The new Jean-Stéphane Sauvaire film is an infernal ride of double-shifts and bullying and death into the belly of the beast, the film pops, hits hard, the image is jumpy, the screams are loud, it’s a pressure-cooker, I came out of there traumatized and a little shaken. This is not the New York City I know. Had an inkling.