BN-777 ⁃ Refine Stats and StatsInterpreter

[sync-by-unito]

The Stats algebra is meant to be a general-purpose utility for surfacing statistics about a computation. For example, it could surface statistics about VRF hits. The initial use-case was to log these statistics to CSV files for post-analysis.

The approach could also be used to replace typical logging. Instead of logging being basic strings (in which data is usually encoded in some arbitrary format), the logs could literally be structured according to stats (and be encoded in a standardized format like key=value or JSON).

The implementation could be improved to use a typeclass pattern on the data that gets logged. For example, ContainsStat[T] which contains a method toStat(t: T): Stat and produces a Stat object that roughly resembles JSON. io.circe.Json could be implicitly adapted, as could com.google.protobuf.Message. For everything else, a custom instance would be created.

Eventually, these stats should be incorporated into as many parts of the system as possible.

┆Issue is synchronized with this Jira Task by Unito