zstd was recommended for the base layer only, due to its CPU requirements. That was a misreading on mhy behalf. lz4 gets ~5% better compression than snappy with ~30% faster performance. zstd does ~25% better than lz4 yet at ~30% of the performance.
Moves explicitly to zstd. RockDB recommends zstd, or at least lz4 over snappy, and this minimizes which dependencies we pull in.
It's needed by the processor and tributary (coordinator).
