The Chicago Board of Education has reached a settlement two decades in the making, resolving a dispute believed to be the longest-lasting case in the Cook County Circuit Court. The board agreed this week to a $2 million settlement with a class of former Chicago Public Schools principals who sued, alleging they were fired under a 1989 law since deemed unconstitutional. The lawyer representing the principals said he believes the suit is the longest-lasting case in the court, one involving a long journey between levels …