We need 1.64 to bump `clap` to `4.1`. We don't really need to upgrade
to that, but being on an older version causes minor confusions like
#1393. Rust 1.64 is very close to 6 months old at this point.
Running `cargo fmt` while you're working in an editor means that you
may lose changes because of a race:
1. Your editor reads version X of file
2. `cargo fmt` reads version X
3. You save version Y from your editor
4. `cargo fmt` saves version Z, replacing Y
It can be confusing that the lib crate is not tested when you run
`cargo test` without `--workspace` from the root directory. Also,
`nextest` is a non-obvious quality-of-life improvement, so let's
suggest that.
