Move LayoutBitset to its own module (#1567) #583

Job	Run time
Pass MSRV values to other jobs	3s
clippy/stable	23s
format/nightly	13s
nostd/thumbv6m-none-eabi/stable	15s
miri	11m 12s
docs/nightly	21s
cross_test/i686-unknown-linux-gnu/stable	1m 56s
cargo-careful	1m 38s
cross_test/s390x-unknown-linux-gnu/stable	8m 34s
blas-msrv	48s
tests/1.64.0	3m 32s
tests/stable	2m 25s
tests/nightly	2m 42s
tests/beta	2m 20s
conclusion	2s
	36m 24s

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