SPRINGFIELD — The doorway leading from the Court of Dreams basketball gym at the Naismith Basketball Hall of Fame used to be just that: a door visitors walk through. Now, it’s the Champions Tunnel, with lights and basketballs, meant to mimic the feeling of being a New York Knick or UCLA Bruin coming off the court after cutting down the net and hosting a trophy. The Naismith Memorial Hall of Fame showcased its newly renovated museum store Tuesday.