By default, `rustfmt` persists the import granularity. In practice, most
Rust code has import granularity "Module" due to LSP's actions.
"Item" gets rid of import groupings and achieves cleaner diffs and
better conflict resolution. Better greppability is a positive side
effect.
Note: it's an unstable rustfmt feature. `cargo +nightly fmt` must be
used instead of `cargo fmt`.