Add experimental live train processor testing system
- This runs real-world TRACKERNET-TRAIN objects through a deterministic log printing system which adds events to a log as they get generated, and keeps track of updated slots (etc).
- The idea is we can smoke test this part of the train processing code (which otherwise is just tested in prod...), and also keep track of when breaking changes are made to it.
- (A previous version of this change used human-readable TRACKERNET-TRAIN logs, but that takes lots of space and isn't really readable anyway, so it was switched to conspack)
- We only have one small little XR test to start us off.