Add a floating layer

[zakj]

Windows in the floating layer are tracked by their window id in is_floating, and persisted across restarts/reloads via hs.settings. The new toggle_floating action can be used to flip the focused window between floating and tiled state.

Would love any feedback here!

Fixes #24.

[mogenson]

Thanks for the PR! Let me try this out.

Do you have to send the floating window to front or send the tiled windows to back while dragging floating windows / switching tiled windows in order to keep the floating windows on top and visible?

[zakj]

Do you have to send the floating window to front or send the tiled windows to back while dragging floating windows / switching tiled windows in order to keep the floating windows on top and visible?

I am treating this like less of a discrete layer than a per-window-id ignore list, since that's primarily my use case. I tried bringing all of the floating windows to the front when focusing one of them, and it felt wrong to me.

One potential awkwardness with this approach is that adding a window to the floating list and then focusing a tiled window does not bring all the other tiled windows to the front; so you can end up with a mix of tiled windows above/behind floating windows. In practice so far this feels more macOS-like, but perhaps less PaperWM-like.

[mogenson]

Looks good to me! I haven't found any issues when using this for a bit. I don't think there's a good way to keep floating windows on top of tiled windows. hs.window:raise() can be buggy and steal focus (despite what the docs say). I think raising every floating window after any tiling action would be too chaotic.

Before I merge, could you please squash your commits into just one and also update the example keybindings in the README: https://github.com/mogenson/PaperWM.spoon?tab=readme-ov-file#usage

[zakj]

Done, thanks!