Giant clouds of smoke rose from a 7-alarm fire that destroyed a warehouse and floated across Brooklyn and into Manhattan on Saturday — a day so cold that water trickling across the helmets of a small army of firefighters quickly froze. One person standing outside the building as firefighters did their work was treated for smoke inhalation at the scene but refused further treatment, authorities said. About 275 firefighters stayed on the fire’s perimeter, training streams of water at flames and smoke fueled by paper inside the storage facility in the Williamsburg neighborhood.