Adress the post-merge comments from #2486, which found a doc comment
inaccurate and to not blindly ignore `-j 0` which would've worked until now.
I've also reduced the default `jobs` size to one, as it's user-visible configuration
which determines how many processes should run.
Thanks to @necauqua the controversial `unsafe` usage was already removed.
I've omitted to change `revisions` from an Vec to a RevisonArg for the moment,
as I will keep working on the file anyway.
Remove a couple of unnecessary unsafes:
- The NonZeroUsize is a constant where the unwrap will optimize away
anyway and we don't have an unsafe without any good reason there :)
- The other two were simply not needed, lifetimes worked fine, maybe
Rust became better since that code was written? NLL? Anyway, they're
gone now
This also adds `jobs`, the argument reading the thread count to use and `shell_command`.
While we're at it, make `execute` a no-op and teach `run` to resolve the passed revsets.
I also fixed my misunderstanding of `Clap` which makes
`jj run 'echo hello world' -r 'mine() & ~origin@remote' --jobs 4` parse correctly.
Also contains a small fix in the `pre-commit` example for it.
