Add model training, export, and read-only inference

[Kaushik-Kumar-CEG]

Adds model training, export, and read only inference to the package

This includes:

• DeBERTa BIOES/CRF training from the generated dataset
• best-checkpoint selection using validation F1
• strict dataset, model-state, and artifact validation
• offline reload before publishing a final model
• CRF and optional ONNX export
• read-only phrase prediction without changing ScanCode rules or files

Final run results:

• validation F1: 0.9008
• test F1: 0.8766
• test precision: 0.8748
• test recall: 0.8784
• test exact match: 0.8197
• invalid BIOES paths: 0

Predictions are candidates and still require human review. The uploaded model was downloaded and validated again successfully

The ScanCode Toolkit version is in aboutcode-org/scancode-toolkit#5222