British stars George MacKay and Rosy McEwen can admit: Mission was one of the least conventional shooting experiences they’ve ever had. It also happened to be one of the most liberating. Director Paul Wright (Arcadia) throws caution to the wind in his latest feature film, set to premiere in competition at Edinburgh Film Festival on Saturday. The Glasgow-set Mission follows Dylan (MacKay), a young Scot who has reached the end of his tether with a dead-end job and lonely, unfulfilling existence. Over the course of a week, he seeks meaning in the wake of extreme chaos — such as breaking a monkey out of the local zoo, attacking a police…