SPRINGFIELD — Six months ago, the state’s top justices unanimously wrote there was “simply no way” changes to public worker pensions squared with the state constitution, which says benefits “shall not be diminished or impaired.”This morning, lawyers for the city of Chicago and two of its pension funds tried to convince them otherwise.It proved challenging.In arguments that lasted about 50 minutes, the city’s lawyers fielded about 16 questions — most of them from Justices …