[UI] Flickering on VisionPro, iPad and iPhone

[karlcow]

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Bug

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There is a flickering effect on GitHub on the PR view.

Steps to reproduce:

1. With an iPhone
2. Go to https://github.com/swaggest/rest/pull/149/files
3. Tap on Aa on the UI and tap on the small a to make the zoom at 85%.
4. Put the phone in landscape mode.
5. Scroll down and up

Result:
The header is flickering

This seems to come from this section of the code.

        function y(t=!1) {
            for (let e of d)
                if (e.element.offsetHeight > 0) {
                    let {element: n, placeholder: i, top: o} = e,
                        l = n.getBoundingClientRect();
                    if (i) {
                        let s = i.getBoundingClientRect();
                        n.classList.contains("is-stuck") ? s.top > S(n, o) ? h(e) : w(e) : l.top <= S(n, o) ? m(e) : t && w(e)
                    } else
                        l.top - S(n, o) < .1 ? m(e) : h(e)
                }
        }

the fuzzFactor is set to 0.1 in l.top - S(n, o) < .1 ? m(e) : h(e)

It should probably be set to 1 to avoid the flickering.

This is happening because sometimes for certain zoom levels it hits some sub-pixels quantity.
The fractional sizes happen because in WebKit/WebCore, subpixel scroll offsets are not stored.

Hope it helps.