fix: respect scroll-margin and scroll-padding in scrollTo

[clementroche]

Summary

• Account for scroll-margin on target elements and scroll-padding on the scroll container when calculating scroll positions in scrollTo()
• Aligns Lenis behavior with native Element.scrollIntoView()
• Uses getComputedStyle() only when scrolling to a DOM element (no perf impact on coordinate-based scrolls)

Fixes #503
Fixes #196

Test plan

• Open playground scroll-margin example
• Verify elements with scroll-margin land at the correct offset
• Verify containers with scroll-padding are respected
• Verify initial hash navigation respects offsets
• Verify no regression on scrollTo() with numeric targets

[feledori]

reading from scrollmargins and paddings should not trigger reflows so this looks good!