Remove `array::UnsafeCellSlice`, use `unsafe_cell_slice` crate #550

Job	Run time
build_and_test_macos (macos-13)	3m 17s
build_and_test_windows	4m 50s
clippy	1m 18s
build_and_test_macos (macos-latest)	1m 26s
build (stable, --features "")	49s
build (stable, --all-features)	1m 57s
build (stable, --no-default-features)	46s
codecov	1m 59s
fmt	24s
minimal-versions	1m 11s
build (1.76, --features "")	54s
semver	1m 6s
test	3m 36s
build (1.76, --all-features)	1m 35s
build (1.76, --no-default-features)	43s
build (beta, --features "")	54s
build (beta, --all-features)	1m 27s
build (beta, --no-default-features)	1m 0s
build (nightly, --features "")	1m 0s
build (nightly, --all-features)	1m 38s
build (nightly, --no-default-features)	53s
	32m 43s

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