Add `half::f16` and `half::bf16` support #557

Job	Run time
clippy/stable	18s
Pass MSRV values to other jobs	4s
miri	10m 53s
format/nightly	15s
nostd/thumbv6m-none-eabi/stable	56s
cargo-careful	2m 14s
cross_test/s390x-unknown-linux-gnu/stable	9m 38s
cross_test/i686-unknown-linux-gnu/stable	2m 18s
docs/nightly	27s
blas-msrv	1m 7s
tests/stable	2m 28s
tests/1.64.0	5m 34s
tests/beta	2m 39s
tests/nightly	2m 59s
conclusion	2s
	41m 52s

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