### What
This PR tries to reduce side effects by:
- Restores the `tar` command to its original state
- Narrow the ~/.cache directory to just nix and devbox

### Why
We are using `chmod u+s "$(command -v tar)"` to setuid on tar (This is
needed because we are caching `/nix/` and other directories outside of
`~`, which is owned by `root`)

This has a problem where it changes the parent directory of
`~/.cache/nix` to be owned by `root` instead of `runner`.

I thought #22
had fixed it, but we ran into similar issues when we use a go cache on
top of the devbox cache.

### Caveat
Cache enabled on self hosted Linux may stop working