perf(scroll-state): remove AnimationFrames loop

[fvarano]

This utility uses requestAnimationFrame to continuously update arrivedState, which has quite a big overhead.

This PR removes continuous requestAnimationFrame loop that caused forced reflows by calling getComputedStyle() every frame. Replace with opt-in MutationObserver for dynamic content scenarios.

The original useScroll utility from Vue does not, instead it provides an optional observe option.

These are (naive) profiles on the docs page of this utility, which are slightly skewed to the old version, since that one is on a production build, while the website hosted locally is not:

Before:

After:

Cannot run tests locally, at the moment, but this utility does not have specific tests.

Pull request checklist

• Code is formatted and linted (pnpm lint, pnpm format)
• Types pass (pnpm check)
• Tests pass locally (pnpm test)
• Docs updated if applicable (content + demo)

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Latest commit: 9be7924

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[kraktus]

Cannot run tests locally, at the moment, but this utility does not have specific tests.

FYI, it's most probably due to nodejs 25, had the same issue

for runed/ contribution, tests failing on node25
vitest-dev/vitest#8757
nodejs/node#60303

using nodev24 resolved it, but as you said it's not important if you don't add tests