Use Criterion for benchmarks

[james7132]

This PR changes the benchmarks for the crate to use Criterion instead of the default benchmark harness, as well as added a few more common operations to ensure it covers more of the common operations for the crate.

[james7132]

CI is failing because criterion cannot compile on 1.39 due to a dependency using the 2021 edition. This is resolvable by:

• Bumping the MSRV to 1.56 when the 2021 edition was introduced.
• Moving the benchmarks into it's own crate so that criterion isn't in the dev-dependencies.

I'm favoring the second choice here since this seems like an arbitrary reason to bump the user facing MSRV. Though that said, 1.56 is also when they added the rust-version Cargo.toml field, which lets us enforce the MSRV in a salient user-facing way.