fix: address the remaining "boring" clippy lints

[rockstar]

This patch addresses the remaining "boring" clippy lints, i.e. the lints that can be fixed at least partially with cargo clippy --fix but don't fundamentally change the shape or meaning of the code it changes. The remaining clippy exceptions require more scrutiny than I think is appropriate for a bundled PR like this.

Each clippy lint is addressed in its own commit, so they can be looked at individually and backed out if need be.

[njsmith]

nice! thanks for the diligent breakdown