inout: use `doc_auto_cfg` (#1118) #1715

Job	Run time
build (1.41.0, thumbv7em-none-eabi)	13s
build (1.41.0, wasm32-unknown-unknown)	21s
build (stable, thumbv7em-none-eabi)	6s
build (stable, wasm32-unknown-unknown)	7s
test (1.41.0)	13s
test (stable)	5s
minimal-versions / minimal-versions	16s
	1m 21s

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