Add tests for `Array::cast_slice_from_core(_mut)` #380

Job	Run time
doc	28s
coverage	30s
careful	59s
miri (x86_64-unknown-linux-gnu)	46s
miri (s390x-unknown-linux-gnu)	1m 0s
build (1.85.0, armv7a-none-eabi)	1m 20s
build (stable, wasm32-unknown-unknown)	1m 20s
build (1.85.0, thumbv7em-none-eabi)	1m 21s
clippy	21s
build (1.85.0, wasm32-unknown-unknown)	1m 22s
rustfmt	15s
test (stable)	40s
test (1.85.0)	47s
build (stable, thumbv7em-none-eabi)	1m 22s
build (stable, armv7a-none-eabi)	1m 19s
	13m 50s

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