Dynamic Size For Dank Bar

### Feature Description

Add Ability To Have Dynamic Size Of Dank Bar Similar To The Dock.

### Use Case

Won't Cover Entire Portion Of The Screen Even If There Are Only Few Items.

### Compositor(s)

- [x] All compositors
- [x] Niri
- [ ] Hyprland
- [ ] MangoWC (dwl)
- [ ] Sway
- [ ] Other (specify below)

### Proposed Solution

Similar TO The Dock

### Alternatives/Existing Solutions

Dock's Implementation Of Dynamic Size.

The issue names no files or tests. Start by comparing the dock's dynamic-size implementation with the bar sizing logic, then check how sizing behaves for the listed compositors; done means the bar no longer spans the full screen when it contains only a few items while preserving the expected behavior across supported compositors.

Written by the indexing model from the issue text.