Photo-Illustration: Intelligencer; Photos: Getty Images After months of seemingly endless mailers, television ads, and door knocks from intrepid canvassers, New Yorkers will head to the polls Tuesday to cast their ballots in some of the most highly watched congressional elections in the country this year. Incumbents like Dan Goldman and Adriano Espaillat are looking to fend off progressive challengers, while open seats left by retiring fixtures like Jerry Nadler and Nydia Velázquez have