Down by seven with just over a minute left, Karl-Anthony Towns had a wide-open three from the top of the key, a chance to cut the Knicks deficit to four and make it interesting. But he airballed. It was fitting, and the MSG crowd rained boos down on the court. This is more than a rut. The Knicks — without Jalen Brunson and Josh Hart on Saturday — are beginning to spiral, as they fell 106-99 to the Suns at Madison Square Garden. “You don’t ever want to have boos, but at the end of the day, the