async-signature: `no_std` support (#1544) #2038

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	1m 3s
build (1.65.0, wasm32-unknown-unknown)	1m 12s
minimal-versions	42s
build (stable, thumbv7em-none-eabi)	16s
build (stable, wasm32-unknown-unknown)	22s
test (1.65.0)	1m 10s
test (stable)	21s
	5m 6s

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