feat: ScrollOffsetController supports scrollToTop

[GeekTree0101]

Description

Adds a scrollToTop() method to ScrollOffsetController.

This method allows users to easily animate the scroll position to the top of the list without needing to manually specify offset = 0.0. It improves code readability and provides a convenient abstraction for a common use case.

Before:

// N/A

After:

await scrollOffsetController.animateScroll(
  offset: -scrollOffsetController.currentScrollOffset,
  duration: Duration(milliseconds: 300),
);

Example

await scrollOffsetController.scrollToTop(duration: Duration(milliseconds: 300));

This PR introduces no breaking changes and simply wraps the existing animateScroll API with a helper method.

Related Issues

N/A

Checklist

• I signed the CLA.
• All tests from running flutter test pass.
• flutter analyze does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

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