Which benchmarks should be included (dataset + split + metric)?

[sgbaird]

I'm planning to incorporate the three benchmark datasets, splits, and metrics from CDVAE. I'm also planning to incorporate mp-time-split (gh) as a dataset+split and use the same metrics from CDVAE. See sparks-baird/xtal2png#12

Not sure if the metrics should be in a separate repository from the dataset/split interface + leaderboard. Probably best to keep it altogether, might be too fragmented otherwise. Should be lightweight enough that it shouldn't matter whether it's separate or not from a dependency perspective.