Diamonds are the New York City Ballet’s best friend, or so it would seem after their season-opening performance on Sept. 22 of George Balanchine’s Jewels, culminating in a radiant display by its raven-haired principal, Mira Nadon, dancing the role originated by Suzanne Farrell in 1967. Nearly 60 years after its wildly successful premiere, which brought star ballerinas Violette Verdy, Mimi Paul, Patricia McBride, and Farrell to even higher acclaim, Jewels remains one of the company’s most beloved pieces, yet among its most challenging artistically.