EUGENE, Ore. (Reuters) – Armand Duplantis brought down the curtain on the World Championships in stunning fashion on Sunday, breaking his own pole vault world record in the final act of the 10-day track and field meet in Eugene. After the United States claimed emphatic victories in both the men’s and women’s 4×400 metre relays, Duplantis took centre stage and duly delivered a perfect finale for the first championships on American soil. The Swede sailed over 6.21 metres to surpass his previous mark by one centimetre – set in March en route to winning gold at the World Indoor Championships – and…