By Gabrielle Tétrault-Farber and Yew Lun Tian BEIJING (Reuters) – Mixed doubles curling opened competition at the Beijing Winter Olympics on Wednesday as the shadow of war in Ukraine, and the impending arrival of Russian President Vladimir Putin, loomed over an event already transformed by the coronavirus pandemic. China and Britain claimed victories in the “Ice Cube”, where American swimmer Michael Phelps won eight gold medals at the 2008 Summer Olympics when it was known as the “Water Cube”, opening the action in the Games which will last until Feb. 20 in front of crowds made sparse by COVID…