refactor(simd): Phase 4 — extract scalar backend to src/simd_scalar.rs #375

Job	Run time
Pass MSRV values to other jobs	3s
nostd/thumbv6m-none-eabi/stable	27s
hpc-stream-parallel/rayon	1m 24s
native-backend/stable	8m 25s
format/stable	22s
clippy/1.95.0	40s
docs/nightly	0s
miri	0s
cargo-careful	0s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
tests/1.95.0	10m 44s
blas-msrv	1m 7s
tests/stable	11m 15s
tests/beta	11m 33s
conclusion	-1s
	45m 59s

Provide feedback