code: function evaluateCoefficientSum(node) {
    // the node is now always a * node with the left child the coefficent sum
    // e.g. (2 + 4 + 5) and the right node the symbol part e.g. x or y^2
    // so we want to evaluate args[0]
    const coefficientSum = clone(node).args[0];
    const childStatus = evaluateConstantSum(coefficientSum);
    return Node.Status.childChanged(node, childStatus, 0);
  }
docs: Given a node of the form (2 + 4 + 5)x -- ie the coefficients have been grouped for adding -- add the coefficients together to make a new coeffient that is a constant or constant fraction.