[EuiDualRange] Migrate from class to function component

`EuiDualRange` provides a dual-handle range slider for selecting a value range. Supports tooltips, ticks, levels, and input fields.

- **File:** `components/form/range/dual_range.tsx`
- **Class size:** 513 lines
- **State:** `id`, `isPopoverOpen`, `rangeWidth`
- **Lifecycle:** None

**Migration notes:**

Largest single class component despite having no lifecycle methods. The complexity is in the extensive drag interaction logic, value clamping, and coordination between two range handles. No lifecycle simplifies migration but the sheer size requires careful review.

**Acceptance criteria:**

- [ ] Convert to function component with hooks
- [ ] Maintain dual-handle drag interaction
- [ ] Maintain value clamping and validation
- [ ] All existing tests pass