feat(simd): BF16x16 + F16x16 SIMD vectors + slice ops (#126, sprint W… #233

Job	Run time
native-backend/stable	50s
Pass MSRV values to other jobs	3s
format/stable	31s
nostd/thumbv6m-none-eabi/stable	48s
docs/nightly	53s
clippy/stable	35s
cargo-careful	38s
miri	29s
cross_test/s390x-unknown-linux-gnu/stable	1m 43s
cross_test/i686-unknown-linux-gnu/stable	1m 55s
blas-msrv	1m 1s
tests/stable	1m 0s
tests/beta	1m 5s
tests/1.64.0	1m 0s
conclusion	-1s
	12m 30s

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