Moves the parsing logic that will be shared by some upcoming scripts out into a separate module.
There's still just as much duplication between the JSON parser and the grpc parser as there was before, but this should at least prevent further duplication of this logic.
This also adds some proper documentation for what each of the stats means.
Doesn't ever seem to happen, but in case it does in the future, treat that case as just unscheduled. This way, the unclassified ping loss (AKA "Beta downtime") can be computed from the totals.
