darwin: switch back to amethyst

[DavSanchez]

Aerospace is very promising but still seems a bit immature for some of my use cases. I'm giving it some more time to see if I adapt, but leaving this PR open to switch back if needed.

For future reference, to see when they are fixed, the issues that I have noticed are:

• Native tabs in general are not handled well (e.g. Preview with many documents open): Native macOS Big Sur tabs are considered windows nikitabobko/AeroSpace#68
  • Accordion mode with a window for each document would work reasonably.
• Apps that are not tiled like VLC (lacks app ID): Some processes don't register in list-apps or list-windows nikitabobko/AeroSpace#575
• It has some resource usage issues that have impacted me as well: High cpu usage for WindowServer process nikitabobko/AeroSpace#154.
  • This happens without Aerospace being enabled and the process doesn't seem to reference anything from the Nix store, something else is going on but probably the Aerospace authors can help...