inout

block-buffer: improve safety comments, use `MaybeUninit` for internal… #568

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	1m 40s
build (1.65.0, wasm32-unknown-unknown)	1m 29s
test (1.65.0)	1m 29s
build (stable, thumbv7em-none-eabi)	33s
test (stable)	9s
build (stable, wasm32-unknown-unknown)	10s
minimal-versions / minimal-versions	16s
	5m 46s

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