If Cristina Spiridakis is doing her job right, you wouldn’t know she had a job at all. That is to say, her work as the costume designer on HBO’s “High Maintenance” is as authentically New York as a morning commute on a packed F train or dollar dumplings in Chinatown. But for Spiridakis, who came aboard the series for its fourth season (premiering Feb. 7), the naturalism of her designs is anything but effortless, particularly considering the show’s vignette style, in which every episode introduces at least one new character. Here’s how she works with creators Ben Sinclair and Katja Blichfeld to achieve looks as specific as every city block, and how what she does is an extension of what the actor does.