feat(simd): real WASM SIMD128 backend (fill simd_wasm.rs scalar scaffolding) #581

Job	Run time
clippy/1.95.0	45s
format/stable	21s
hpc-stream-parallel/rayon	1m 34s
Pass MSRV values to other jobs	2s
tier4-avx512-check	28s
nostd/thumbv6m-none-eabi/stable	25s
native-backend/stable	7m 54s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
nightly-simd-polyfill	0s
docs/nightly	0s
miri	-1s
cargo-careful	-1s
blas-msrv	1m 0s
tests/beta	12m 25s
tests/1.95.0	9m 15s
tests/stable	11m 0s
conclusion	0s
	45m 7s

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