[Example] Restart `selfplay` from the last step

[sotetsuk]

https://api.wandb.ai/links/sotetsuk/0t8pjyb4

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (99f9a08) 88.08% compared to head (214cc58) 88.08%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1116 +/- ## ======================================= Coverage 88.08% 88.08% ======================================= Files 60 60 Lines 5918 5918 ======================================= Hits 5213 5213 Misses 705 705 ```

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