Add `#[required(<count>)]` #3534

Job	Run time
compute-jobs	4s
build-linux / linux test	3m 56s
build-linux / linux lint-deps	1m 46s
build-linux / linux lint	1m 0s
build-linux / linux coverage	4m 6s
build-linux / linux test-miri	6m 47s
build-linux / linux test-ops	6m 5s
build-linux-arm / linux-arm test	5m 45s
build-linux / linux test-publish	1m 40s
build-linux-arm / linux-arm test-miri	11m 39s
build-linux-arm / linux-arm lint	1m 34s
build-linux-xl / linux-xl test-valgrind	26m 31s
build-macos / macos lint	1m 2s
build-macos / macos test	4m 17s
build-windows / windows lint	3m 42s
build-windows / windows test	10m 53s
success	1s
	1h 30m 48s

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