feat: add `BitVec.cpop` and lemmas #48061

Job	Run time
configure	8s
build / Linux Lake	6m 25s
build-secondary / macOS aarch64	53m 38s
build-secondary / Linux release	55m 2s
Build matrix complete	4s
release	0s
release-nightly	0s
	1h 55m 17s

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