Pinchas Zukerman’s abrupt decision to skip out on the second half of the sesaon with his National Arts Center Orchestra is puzzling. “During the 5½ months he won’t be performing with the NACO, Zukerman is booked for dozens of guest appearances with 14 orchestras on three continents. In sum, Zukerman is skipping out of his salaried gig, but keeping all the freelance work.” Doesn’t sound like a man “taking a sabbatical”…