Cape Cod: In many ways the decade-long battle surrounding the proposed Nantucket Sound wind farm has always been a stand-in for a much larger debate over the future of the nation’s energy policy. But after countless arguments for and against Cape Wind, perhaps nowhere have the basics of the broader dispute been more distilled than in a makeshift hearing room above Boston’s South Station. The state Department of Public Utilities is midway through two weeks of hearings to determine whether …