style: fix a pile of "dumb but fair" clippy lints #835

Job	Run time
docs	2m 40s
just check	4m 14s
netlify_dryrun	2m 52s
just clippy	4m 38s
rustfmt	36s
cargo miri test (host)	1m 6s
just test	2m 41s
cargo build mnemos-d1	2m 0s
cargo build mnemos-esp32c3-buddy	1m 19s
cargo build mnemos-x86_64-bootloader	2m 6s
	24m 12s

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