It’s champagne and caviar tonight for billionaire hedge funderSteven A. Cohen, who received the official go-ahead to build a massive, six-story, single-family mansion at145 Perry St. Wednesday. The Landmarks Preservation Commission voted almost unanimously in favor of the plan despite outcry from local residents and, most notably, Andrew Berman of theGreenwich Village Society for Historic Preservation who had denounced the design in a statement as “starkly modern,” “fortress-like and massive,” and more like a bank or a luxury retail store you’d find in Miami or Los Angeles, not the “simple but charming” Village.