der: conversions from `OctetString(Ref)` to `Vec`/`Bytes` #1422

Job	Run time
build (1.81.0, thumbv7em-none-eabi)	26s
build (1.81.0, wasm32-unknown-unknown)	31s
build (stable, thumbv7em-none-eabi)	26s
build (stable, wasm32-unknown-unknown)	21s
minimal-versions	0s
test (1.81.0)	1m 21s
test (stable)	1m 10s
	4m 15s

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