style: use variables directly in format!()

[caspermeijn]

Prevent clippy warnings like:

error: variables can be used directly in the `format!` string
  --> benchmarks/benches/dataset.rs:40:47
   |
40 |     let mut group = criterion.benchmark_group(format!("dataset/{}", name));
   |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args
   = note: `-D clippy::uninlined-format-args` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::uninlined_format_args)]`
help: change this to
   |
40 -     let mut group = criterion.benchmark_group(format!("dataset/{}", name));
40 +     let mut group = criterion.benchmark_group(format!("dataset/{name}"));
   |