feat(simd): Phase 3 scaffold — NEON tier flavors (baseline / dotprod / bf16) #384

Job	Run time
hpc-stream-parallel/rayon	1m 21s
clippy/1.95.0	41s
format/stable	21s
native-backend/stable	8m 14s
nostd/thumbv6m-none-eabi/stable	26s
Pass MSRV values to other jobs	4s
tier4-avx512-check	27s
miri	0s
cargo-careful	0s
docs/nightly	0s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
blas-msrv	52s
tests/stable	12m 13s
tests/1.95.0	12m 7s
tests/beta	11m 38s
conclusion	-1s
	48m 23s

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