…ts in benchmarks (#17222)

# Objective

- Commands like `cargo bench -- --save-baseline before` do not work
because the default `libtest` is intercepting Criterion-specific CLI
arguments.
- Fixes #17200.

## Solution

- Disable the default `libtest` benchmark harness for the library crate,
as per [the Criterion
book](https://bheisler.github.io/criterion.rs/book/faq.html#cargo-bench-gives-unrecognized-option-errors-for-valid-command-line-options).

## Testing

- `cargo bench -p benches -- --save-baseline before`
- You don't need to run the entire benchmarks, just make sure that they
start without any errors. :)