Hedge funds that specialize in distressed investing have been kicking the tires of the New York taxi market after prices for medallions plummeted in the face of competition from ride-hailing upstarts. Marblegate Asset Management LLC, a Greenwich, Conn., hedge-fund firm, decided to place a big bet, and over the past year or so has scooped up around 300 medallions for a total price of more than $50 million, according to people familiar with its strategy.