Add SPR implementation to atari_100k lab

[MaxASchwarzer]

I'd like to add support for SPR to the Atari 100k lab project. My implementation is mostly siloed to minimize changes to the existing algorithms. SPR needs a custom model-based style replay buffer that returns subtrajectories, and a version of noisy nets that allows noise to be toggled on and off within a function, both of which are included.

This implementation performs a bit better than the original version; I found median 0.45 over 100 seeds, compared to 0.395 for the original.

@psc-g @agarwl

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[MaxASchwarzer]

@googlebot I signed it!