AtomicCell: Use atomic-maybe-uninit #3099

Job	Run time
features (msrv)	41s
test (1.63, ubuntu-latest)	10m 45s
features (nightly)	24s
careful	5m 11s
test (1.63, windows-latest)	10m 35s
clippy	18s
test (stable, ubuntu-latest)	10m 3s
codegen	4s
test (stable, windows-latest)	10m 19s
dependencies	20s
docs	12s
test (nightly, ubuntu-latest)	9m 38s
loom	49s
test (nightly, windows-latest)	10m 29s
miri (channel)	10m 46s
test (nightly, ubuntu-latest, i686-unknown-linux-gnu)	10m 41s
rustfmt	2s
miri (others)	10m 49s
test (nightly, ubuntu-latest, armv7-unknown-linux-gnueabihf)	10m 45s
san	10m 45s
test (nightly, ubuntu-latest, armv5te-unknown-linux-gnueabi)	10m 45s
shellcheck	9s
test (stable, ubuntu-latest, sparc64-unknown-linux-gnu)	9m 7s
	2h 23m 37s

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