feat: add range slider mode

[draggie]

Summary:

Adds an optional two-thumb range mode to Slider without changing the existing single-thumb native slider path.

The new mode is enabled with range and accepts values, minimumRange, onValuesChange, onRangeSlidingStart, and onRangeSlidingComplete. It renders a JS range control with two thumbs, selected-track highlighting, step/limit clamping, non-crossing thumb behavior, disabled handling, thumb images/tints, and basic accessibility increment/decrement support.

This also updates TypeScript declarations, README API docs, and the iOS/Android/Web example lists with a Range slider example.

Closes: #25

Test Plan:

• cd package && npx tsc --noEmit
• cd package && npm test -- --runInBand --no-watchman
• cd package && npm run lint
• cd package && npm run prepare
• Refreshed the example app package copy with cd example && npm run refresh-package and verified the copied package contains RangeSlider and the range branch.