Assembly Speaker Sheldon Silver has spun the 9/11 lawsuits into gold. Ground Zero workers are on the hook to pay steep interest on money their lawyers borrowed from a group of investors that include Silver and his law partners, The Post has learned. Silver's partners at the Weitz & Luxenberg law firm are top board members of a business that quietly loaned money at 18 percent a year to the law firm representing some 9,800 Ground Zero workers with toxic-illness suits against the city. Silver personally invested an undisclosed sum -- but at least $50,000 -- in Counsel Financial Services,...