By Thomas Neumann The longtime Blackhawks defenseman, a two-time Norris Trophy winner, announced his retirement Tuesday. Longtime NHL defenseman Duncan Keith, a three-time Stanley Cup champion with the Blackhawks, announced his retirement Tuesday. Keith, 38, is a two-time Norris Trophy winner as the league’s top defenseman, and he won two Olympic gold medals with Team Canada. A second-round pick in the 2002 NHL draft, Keith played the first 16 years of his NHL career with Chicago before asking to be traded closer to home in Western Canada in 2021. He played last season with Edmonton. Keith won…