Use an lru cache to drop duplicate beacons (#453) #1201

Job	Run time
build (arm-unknown-linux-gnueabihf)	3m 26s
build (armv5te-unknown-linux-musleabi)	3m 39s
build (armv7-unknown-linux-musleabihf)	3m 30s
build (aarch64-unknown-linux-musl)	4m 18s
build (mips-unknown-linux-musl)	3m 45s
build (mipsel-unknown-linux-musl)	3m 40s
build (x86_64-unknown-debian-gnu)	4m 5s
build (x86_64-tpm-debian-gnu)	3m 37s
hygiene	3m 56s
docker_buildx	9m 6s
release	0s
	43m 2s

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