equal method
Implementation
bool equal(Range<T> range) {
if (empty && range.empty) {
return true;
}
final isLowerBoundEqual = _isBoundsEqual(lowerBound, range.lowerBound);
final isUpperBoundEqual = _isBoundsEqual(upperBound, range.upperBound);
return isLowerBoundEqual && isUpperBoundEqual;
}