Use an lru cache to drop duplicate beacons #1197

Job	Run time
hygiene	2m 33s
build (arm-unknown-linux-gnueabihf)	3m 11s
build (armv5te-unknown-linux-musleabi)	2m 41s
build (armv7-unknown-linux-musleabihf)	3m 48s
build (aarch64-unknown-linux-musl)	3m 18s
build (mips-unknown-linux-musl)	3m 7s
build (mipsel-unknown-linux-musl)	4m 1s
build (x86_64-unknown-debian-gnu)	3m 0s
build (x86_64-tpm-debian-gnu)	3m 37s
docker_buildx	11m 28s
release	0s
	40m 44s

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