keeping files outside the work directory across cub reset

[ongardie]

Right now the work directory survives a cub reset and nothing else does. It's easy to come up with things outside the work directory that would be nice to keep. For example:

• ~/.zsh_history is useful so you can search for previously run commands, and it's entirely harmless.
• ~/.config/VSCodium/User/workspaceStorage/ appears to have the editor layout, which can be helpful to quickly pick up where you left off.
• well-behaved download/build caches?

There's no mechanism for this now. I could imagine a pre-reset hook script that would produce a tar file just like the packages do, that then gets seeded back in.

Maybe packages would want to contribute their own files, however. For example, the Rust package might know that the Cargo cache is worth keeping and safe to keep.

And then that opens the question of whether you'd want to be able to do a "harder" reset without this stuff, or without some of this stuff.