save/load ML models

[SCiarella]

This closes #110, by adding a save/load utility for the ML modules using safetensors

Main changes:

• add safetensors as a dependency
• add diffwofost.ml_models.io with:
  • save_model(model, ...)
  • load_model(path, ...)
• store enough metadata to rebuild a saved model
• give models a default checkpoint name based on model structure
• add tests for save/load
• show how to use save/load in hybrid notebook
• add new function to API (docs)

Design choices:

• save_model(model) saves to a default temp location (ignored by git)
• the default filename depends on model class + init kwargs (deterministically)
• so the same model structure reuses the same checkpoint path
• saving again after retraining overwrites that file
• if you want multiple saved variants, you have to pass a custom filename

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
91.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud