By Melissa Jones Galopin Des Champs is on the cusp of becoming a Cheltenham Festival legend after he headlined a 713-1 Willie Mullins four-timer at Leopardstown. Ireland’s top trainer and his dominant horse of its staying division Iived up to the Dublin Racing Festival hype – and are on-course to write their names into history in March. Galopin Des Champs, 4-6 (from evens) to take a second Boodles Gold Cup crown at Gloucestershire’s biggest sporting event, completed a clean sweep of Grade One races for Mullins. “He was the big bullet and he hit the bullseye,” said Paddy Power Irish Gold Cup-wi…