By Andrew McCarty The San Francisco 49ers are on their third quarterback of the season, but still very much in the playoff hunt. More than that, the team has already clinched their division, despite starting a rookie quarterback for the final few games of the season. Former Iowa State standout Brock Purdy has executed the 49ers offense well without making many mistakes. Despite his very competent play so far this season, head coach Kyle Shanahan isn’t making any promises on Purdy’s future. Here’s what he said, via NBC Sports: “I don’t even know what year it is after this season’s over,” Shanah…