Israeli firms boosted New York’s economy by a whopping $13.3 billion and helped fuel nearly 58,000 jobs last year, a new study shows — but the gains could drop if Zohran Mamdani becomes mayor, a CEO warned Monday. About 90% of the billions of dollars and massive job haul from 648 Israeli-founded businesses was focused in the five boroughs, according to findings by the United States-Israel Business Alliance. The CEO of an Israeli biotech company told The Post his business could be another to