Fix new clippy lints

[Swatinem]

Looks like the newer compiler version is more aggressive detecting dead code, and flags a bunch of fields/functions as unused. Some of those are behind feature flags, others might legitimately be unused. However, I just used an allow to quickly unblock other PRs that are failing because of these lints without digging deeper.

Also ran a cargo update for good measure, but not bumping any semver-major dependency versions.