Live updating log viewer

[jjallaire]

Currently the terminal updates in realtime but the log viewer does not (requires an explicit refresh)

To implement this we'll need an efficient side channel to sync transcript events into (as we don't want to push the entire log to S3 just for high granularity event updates). This might take the form of events written alongside logs or alternatively somewhere on the system running the eval if we think that cluttering up the log directory is undesirable.