sha2: provide support for `spki::AlgorithmIdentifier` #676

Job	Run time
minimal-versions / minimal-versions	32s
set-msrv / set-msrv	2s
test (1.74.0)	22s
build (1.74.0, thumbv7em-none-eabi)	18s
test (stable)	23s
build (1.74.0, wasm32-unknown-unknown)	28s
build (stable, thumbv7em-none-eabi)	22s
build (stable, wasm32-unknown-unknown)	14s
	2m 41s

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