Add 3DGS SIMD forward renderer plan #471

Job	Run time
format/stable	20s
nightly-simd-polyfill	49s
Pass MSRV values to other jobs	3s
hpc-stream-parallel/rayon	1m 20s
clippy/1.95.0	43s
native-backend/stable	8m 21s
miri	1m 5s
cargo-careful	41s
docs/nightly	48s
tier4-avx512-check	27s
nostd/thumbv6m-none-eabi/stable	22s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
blas-msrv	49s
tests/beta	11m 4s
tests/stable	10m 55s
tests/1.95.0	11m 15s
conclusion	0s
	49m 2s

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