clearAll method
void
clearAll()
Resets every slide-related field back to its initial state and
disposes the ticker. Called from TreeController._clear (and
indirectly from dispose). The next animateFromOffsets call
recreates the ticker via the existing _ticker ??= ... pattern.
Implementation
void clearAll() {
_ticker?.dispose();
_ticker = null;
_slideByNid = <SlideAnimation<TKey>?>[];
_activeSlideNids.clear();
_xActiveCount = 0;
}