feat: Allow study progress to be saved & resumed (#106)

* feat: Store active study in log/study.jsonl and allow resuming

* Simplify resume logic with load_if_exists=True

* Significantly improve flexibility of study save/load

* Put constructor arguments at the highest precedence

* Review comments

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Co-authored-by: Spiky Moth <spikymoth@pm.me>

.gitignore

@@ -17,3 +17,6 @@ wheels/
 
 # Configuration files
 /config.toml
+
+# Study checkpoints
+/checkpoints/*.jsonl