docs(simd): per-CPU dispatch matrix + Codex review fixes #395

Job	Run time
clippy/1.95.0	42s
nostd/thumbv6m-none-eabi/stable	27s
native-backend/stable	7m 49s
tier4-avx512-check	27s
format/stable	22s
hpc-stream-parallel/rayon	1m 21s
Pass MSRV values to other jobs	2s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	-1s
nightly-simd-polyfill	-1s
docs/nightly	-1s
miri	-1s
cargo-careful	-1s
tests/beta	10m 43s
tests/1.95.0	11m 29s
tests/stable	10m 28s
blas-msrv	1m 1s
conclusion	0s
	44m 46s

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