sha2: provide support for `spki::AlgorithmIdentifier` #305

Job	Run time
minimal-versions / minimal-versions	31s
set-msrv / set-msrv	5s
test (1.71.0)	35s
build (1.71.0, thumbv7em-none-eabi)	17s
test (stable)	28s
build (1.71.0, wasm32-unknown-unknown)	21s
build (stable, thumbv7em-none-eabi)	20s
build (stable, wasm32-unknown-unknown)	12s
	2m 49s

Provide feedback