perf: memoize options/thumbImage and stop mutating on inverted

[pataar]

Summary:

Three marginal-but-easy perf/correctness fixes in the JS layer. No public API changes, no behaviour changes for end users.

1. Memoize options in Slider.tsx — the Array.from(...) call rebuilt the array on every render. Wrapping it in useMemo also restores the effectiveness of StepsIndicator's existing useCallback/useMemo, which currently bust every render because the parent hands them a freshly allocated array.
2. Memoize the resolved thumbImage in Slider.tsx — Image.resolveAssetSource(...) ran on every render. Memoized on props.thumbImage/props.StepMarker.
3. Stop mutating options in StepsIndicator.tsx — options.reverse() mutates the array passed in from the parent in place. Switched to options.slice().reverse(). Mostly a correctness fix; with the parent now memoizing the array, the in-place reverse would also have re-reversed the same array each render.

Test Plan:

• npm test from package/ → 4 suites, 16 tests passing.
• npm run lint from package/ → no new warnings introduced.
• Recommended smoke test in the example app: scenarios with inverted, with non-zero step, and with thumbImage set, to confirm no visual regression.