I couldn't find a built-in functions for min/max value of two or more durations. Similar to [min](https://api.flutter.dev/flutter/dart-math/min.html)/[max](https://api.flutter.dev/flutter/dart-math/max.html) in the [dart:math](https://api.flutter.dev/flutter/dart-math/) library. It would be nice to add those functions to this package. Will you consider a PR to add those functions?
