Yet more preempting of Rust 1.80 lints

[ErichDonGubler]

Connections

Offloading some diff. complexity from #6105.

Description

Fixes more lints that will definitely affect us with Rust upgrades later.

Testing

Things still compile, so woot!

Checklist

• Run cargo fmt.
• Run cargo clippy. If applicable, add:
  • --target wasm32-unknown-unknown
  • --target wasm32-unknown-emscripten
• Run cargo xtask test to run tests.
• Add change to CHANGELOG.md. See simple instructions inside file. Not necessary.

[cwfitzgerald]

What's the problem this is solving?

[ErichDonGubler]

@cwfitzgerald:

What's the problem this is solving?

Individual motivations are already in the OP and individual commits, but to summarize: most of this changes code to add use std::mem::{size_of, size_of_val}, which is intended to head off most of the unused_qualifications warnings that will be introduced by Rust 1.80 adding them to the prelude. See also #6105.