cms

x509-cert: introduce a `builder::AsyncBuilder` trait #860

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	1m 16s
build (1.65.0, wasm32-unknown-unknown)	1m 18s
build (stable, thumbv7em-none-eabi)	26s
test (1.65.0)	1m 11s
build (stable, wasm32-unknown-unknown)	28s
test (stable)	47s
minimal-versions / minimal-versions	52s
	6m 18s

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