`SingleAttestation` implementation (#6488) #1771

Job	Run time
extract-version	1s
build-docker-lighthouse-aarch64	20m 39s
build-docker-lighthouse-x86_64	19m 57s
build-docker-lcli-aarch64	6m 53s
build-docker-lcli-x86_64	6m 39s
build-docker-lighthouse-multiarch	4s
build-docker-lcli-multiarch	6s
	54m 19s

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