You may not know Wet Leg duo Rhian Teasdale and Hester Chambers (yet), but there's been no escaping their infectious, tongue-in-cheek indie-pop hits, which have dominated the airwaves while earning them Grammys, Brits, and the opening slot on Harry Styles' tour. Hanna Hanra meets the free-wheeling duo to talk fun friendship and tearing up the songwriting rule book