For symmetry with @initialize

This behavior is mostly currently achievable with result_callback that you can pass to Typer.callback or Typer.group. There are two deficiencies:

1. The command must be compound. There's no way to finalize a singular command. This makes sense, but it'd be nice if the interface uniformly worked.
2. result_callback is not class aware, so you have to jump through extra hoops to get access to self - namely you need to return it from your subcommands.