Command to define window width when in bsp mode?

I'd like to be able to create hotkeys to size the currently focused window to a particular width, but thus far the closest method I've figured to programmatically resize a window requires floating the window, eg:

```
# change window size to (1920, 1080)
alt + shift - s : yabai -m space --layout float && yabai -m window --resize abs:1920:1080
```

It would be great if there was a method to define the width of the active window, something like this, that would work irrespective of the layout mode:

```
alt + shift - s : yabai -m windowwidth --resize abs:1920
```

Perhaps being able to use a percentage rather than an absolute value would be valuable so that config will work across multiple screen sizes

Start by reproducing the existing `yabai -m window --resize` behavior in bsp mode and trace the window-resize command entry point. Define whether absolute and percentage widths should work without floating, then verify the chosen behavior across supported layout modes and screen sizes.

Written by the indexing model from the issue text.