[codex] Add optional WT peptide prediction

[iskandr]

Summary

• Add TopiaryPredictor(predict_wt=True) to score populated wt_peptide values with the configured MHC model(s).
• Join WT scores back by peptide, allele, length, prediction kind, method, and version so affinity and presentation rows remain aligned.
• Update ranking/API/fragment docs, README, changelog, and bump the package version to 5.10.2.

Closes #123.

Validation

• python -m pytest tests/test_predict_from_fragments.py::TestWtPeptide tests/test_predict_from_variants_refactor.py::TestFragmentColumnsOnVariantPath::test_predict_wt_populates_wt_prediction_columns
• ./lint.sh
• ./test.sh

[coveralls]

coverage: 89.239% (+0.07%) from 89.171% — codex/predict-wt-peptides into master