GREENVILLE, N.C. — As Duke Energy pleaded guilty Thursday in a North Carolina courtroom to nine criminal violations of the federal Clean Water Act, federal prosecutors recounted examples where time and again the nation’s largest electricity company failed to prevent its illegal pollution.Two years before the massive February 2014 spill at a Duke ash dump in Eden coated 70 miles of the Dan River in gray sludge, engineers at the plant twice requested $20,000 from company headquarters to use a robotic camera to …