der: conversions from `OctetString(Ref)` to `Vec`/`Bytes` #855

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	30s
build (1.81.0, wasm32-unknown-unknown)	30s
build (stable, thumbv7em-none-eabi)	23s
build (stable, wasm32-unknown-unknown)	23s
minimal-versions	0s
test (1.81.0)	27s
test (stable)	25s
	2m 38s

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