Summary

Fixes cboulanger#2 — AbstractTrainer.train() (mode 0) previously ignored any Wapiti parameters set via setParams() and always read them from GrobidProperties. This PR completes the fix in two parts:

1. Fix AbstractTrainer.train() to honour instance-level Wapiti parameter overrides

splitTrainEvaluate() (mode 2) and nFoldEvaluate() (mode 3) already used instance fields as overrides. Mode 0 now does the same:

trainer.setEpsilon(epsilon != 0.0 ? epsilon : GrobidProperties.getEpsilon(model));
trainer.setWindow(window != 0 ? window : GrobidProperties.getWindow(model));
trainer.setNbMaxIterations(nbMaxIterations != 0 ? nbMaxIterations : GrobidProperties.getNbMaxIterations(model));

Fully backwards-compatible: when setParams() has not been called, the instance fields default to 0/0.0 and config values are used as before.

2. Expose Wapiti parameters and custom model output path via TrainerRunner CLI

TrainerRunner (the JAR entry point) never called setParams(), so the fix above was unreachable from the command line. New optional flags:

When -modelPath is provided:

• The model is written directly to the specified path (no .new/.old atomic rename).
• An error is raised if the specified path equals the hardcoded default model path.
• All other behaviour (no -modelPath) is unchanged.

Use case

Enables callers constructing a trainer programmatically or via CLI/HTTP to supply runtime Wapiti parameters and write versioned/test model files without modifying grobid.yaml.

Affected files

• grobid-trainer/src/main/java/org/grobid/trainer/AbstractTrainer.java
• grobid-trainer/src/main/java/org/grobid/trainer/TrainerRunner.java

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