chore: apply `unreachable_pub` lint to crates #683

Job	Run time
set-msrv / set-msrv	3s
minimal-versions / minimal-versions	34s
test (stable)	45s
build (1.85.0, thumbv7em-none-eabi)	20s
test (1.85.0)	1s
build (stable, thumbv7em-none-eabi)	26s
build (stable, wasm32-unknown-unknown)	2m 17s
build (1.85.0, wasm32-unknown-unknown)	19s
	4m 45s

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