feat(simd): I8/I16 SIMD vectors + slice-level int ops (sprint A3) #224

Job	Run time
clippy/stable	39s
Pass MSRV values to other jobs	2s
cross_test/s390x-unknown-linux-gnu/stable	1m 47s
format/stable	31s
native-backend/stable	55s
nostd/thumbv6m-none-eabi/stable	39s
cross_test/i686-unknown-linux-gnu/stable	1m 8s
cargo-careful	0s
miri	0s
docs/nightly	0s
blas-msrv	50s
tests/beta	1m 6s
tests/1.64.0	1m 4s
tests/stable	1m 9s
conclusion	0s
	9m 50s

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