Add animation for click button skip, next, back

First! Thank for your package. It saves me a lot of time.
Hope I can help you with this "Request"

--> This is my code
```
...
void animationToPage(int page) {
nextPageIndex = page;
animatedPageDragger = AnimatedPageDragger(
slideDirection: activePageIndex > nextPageIndex
? SlideDirection.leftToRight
: SlideDirection.rightToLeft,
transitionGoal: TransitionGoal.open,
slidePercent: slidePercent,
slideUpdateStream: slideUpdateStream,
vsync: this,
);
animatedPageDragger.run();
}
...

void onPressedBack() {
animationToPage(max(0, activePageIndex - 1));
}

void onPressedNext() {
animationToPage(min(widget.pages.length - 1, activePageIndex + 1));
}

void onPressedSkip() {
animationToPage(widget.pages.length - 1);
}
...
```

The issue shows code for navigation methods (onPressedBack, onPressedNext, onPressedSkip) that call animationToPage. Look at the AnimatedPageDragger class to understand the animation system. The request is to add animation for button clicks; check existing button widgets and see how they trigger page transitions. Test by running the example app and modifying the button handlers to include animation.

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