Unnecessary Instantiation on DefaultGroovyMethods.numberAwareCompareTo

in numberAwareCompareTo()

        NumberAwareComparator<Comparable> numberAwareComparator = new NumberAwareComparator<Comparable>();
        return numberAwareComparator.compare(self, other);

The code inside NumberAwareComparator.compare can be static, so there is no need to create a new Instance of the Comparator every numberAwareCompareTo is called. I suggest extracting the logic into a public static method, and to use that, or anything similar.