changeIndex method
Implementation
void changeIndex({int? newIndex}) {
currentIndex = newIndex;
if (currentIndex! <= 0) {
currentIndex = 0;
} else if (currentIndex! >= stories.length) {
currentIndex = stories.length - 1;
}
animationController.reset();
animationController.duration = currentStory.duration;
_callFunctions(_onIndexChangeds);
}