IntervalDuration class

A custom curve that creates time-based intervals within an animation duration.

IntervalDuration allows you to create animations that start after a delay or end before the full duration completes, using actual Duration values instead of normalized progress values (0.0-1.0).

This is particularly useful for staggered animations or when you need precise timing control based on real time intervals rather than animation progress percentages.

Example:

// Animation that starts after 500ms delay and ends 200ms early
IntervalDuration(
  start: Duration(milliseconds: 500),
  end: Duration(milliseconds: 1800), // out of 2000ms total
  duration: Duration(milliseconds: 2000),
  curve: Curves.easeInOut,
);