…tion

- **Shape:**
    - Transition the scrollbar indicator from a `drawRoundRect` to a `Path` with `addRoundRect`.
    - This allows for independent control over the corner radii of the indicator.
    - Introduce `indicatorRightCornerRadius` to create a squarer shape on the right side while keeping the left side fully rounded, achieving a "squircle" effect when expanded.
- **Animation & Sizing:**
    - Add `indicatorExpandedWidthBoost` to provide a subtle extra expansion during user interaction.
    - The indicator's width animation now accounts for this boost, creating a more dynamic feel.
- **Layout:**
    - The overall component width is now based on the boosted expanded width to prevent clipping during the interaction animation.