Add 3DGS validation benchmark plan #475

Job	Run time
nostd/thumbv6m-none-eabi/stable	26s
native-backend/stable	7m 50s
format/stable	21s
Pass MSRV values to other jobs	2s
clippy/1.95.0	33s
hpc-stream-parallel/rayon	1m 19s
tier4-avx512-check	31s
docs/nightly	52s
cargo-careful	41s
miri	1m 12s
nightly-simd-polyfill	39s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
tests/beta	10m 59s
tests/1.95.0	10m 40s
blas-msrv	51s
tests/stable	10m 43s
conclusion	-1s
	47m 38s

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