Update deps with minimal changes

[lorlouis]

I updated dependencies which required a minimal amount of work to upgrade.

Some of the larger libraries, serde_yaml, hyper, and the Prometheus crates, would require significant code churn to get up to date, so I left them alone for now.

I also updated serde deny's config to v2 format since v1 got dropped a while back.

v2 migration context
EmbarkStudios/cargo-deny#611

I also fixed a few clippy lints/deprecation warnings.

[lorlouis]

It looks like the minimal-versions CI step can't be made to work without upgrading a few significant libraries.
It currently fails on some transitive dependencies which are expecting an older version of the compiler and explicitly declare features which have been stabilised.

Since it won't break this version of the library any more than it currently is, I would suggest merging it anyway, and I'll try to update hyper, tonic and a few other big crates in another patch.