Fix flicker issue on re-render in web implementation of Slider component

[landabaso]

Description

This PR addresses an issue with the Slider component where a flicker effect is visible during re-renders, specifically in the web implementation. The flicker was caused by the width being reset during the layout calculation.

Changes Made

• Modified sliderStyle to set the width only if it is not zero using the conditional spread operator.

  const sliderStyle = { zIndex: 1, ...(width !== 0 && { width }) };

[landabaso]

Oups, one of the tests failed (due to a snapshot comparison). Please let me know if you agree with this PR approach, and I'll update the snapshot accordingly.

[landabaso]

In fact, I am still experiencing flicker issues on iOS and Android. Not setting the width at all (as it was originally) solves the flicker. That is: const sliderStyle = { zIndex: 1 }; However, I assume the width was set for a specific reason, which is why I didn't remove it in my initial approach. Is setting the width strictly needed?

Could you provide some insights on why the width was added, @BartoszKlonowski? This was introduced in PR #555. Setting styles in onLayout can be tricky and may introduce flickering, depending on how parent components handle their children.

Thanks!