Add 3DGS implementation plan index #470

Job	Run time
format/stable	20s
clippy/1.95.0	44s
nostd/thumbv6m-none-eabi/stable	26s
cargo-careful	39s
Pass MSRV values to other jobs	3s
hpc-stream-parallel/rayon	1m 20s
docs/nightly	51s
nightly-simd-polyfill	41s
tier4-avx512-check	31s
native-backend/stable	8m 21s
miri	58s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
tests/beta	11m 22s
tests/1.95.0	10m 34s
tests/stable	10m 27s
blas-msrv	55s
conclusion	0s
	48m 12s

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