docs: update docs for training

[stephantul]

This PR updates all docs to contain the new training options

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
model2vec/inference/model.py	100.00% <100.00%> (ø)
model2vec/persistence/persistence.py	98.86% <100.00%> (+0.04%)	⬆️

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[greptile-apps]

Confidence Score: 4/5

[Low impact] Documentation and test updates for training features.

This PR appears safe to merge, with a non-blocking installation gap in the ONNX examples.

_{Reviews (1) · Last reviewed commit: "update results" · Reviewed by Greptile}