Reduce game log size

[taylorhansen]

Each game log file costs around 500kb-1mb currently. During long training runs this can accumulate dozens of gb of text files, most of which aren't really that useful to examine unless there's a bug or some extra analysis that's needed after the fact, and for large numbers of threads this may cause a disk I/O bottleneck.

Modify the game simulator threads to keep logs in memory and only write to disk at the end if there's an error, otherwise discard them. This might cause a big memory hit for multithreaded setups but likely still manageable.

Since some bugs are silent, it may also be useful to store a (random?) sample of un-errored logs, e.g. all 2^n-numbered games which should greatly stem disk usage growth for longer training runs.