serdect: safer bytes handling #2470

Job	Run time
derive (1.65.0)	4m 44s
build (1.65.0, thumbv7em-none-eabi)	7m 50s
test (i686-unknown-linux-gnu, ubuntu-latest, 1.65.0, sudo apt update && sudo apt install gcc-mult...	30m 1s
build (1.65.0, wasm32-unknown-unknown)	6m 41s
test (i686-unknown-linux-gnu, ubuntu-latest, stable, sudo apt update && sudo apt install gcc-mult...	21m 18s
build (stable, thumbv7em-none-eabi)	2m 31s
build (stable, wasm32-unknown-unknown)	2m 38s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.65.0)	25m 25s
test (x86_64-unknown-linux-gnu, ubuntu-latest, stable)	16m 55s
derive (stable)	26s
minimal-versions / minimal-versions	14m 44s
	2h 13m 13s

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