refactor(xgboost): migrate to callback-based early stopping for API 3.x compatibility

refactor(xgboost): migrate to callback-based early stopping for API 3.x compatibility

- Replace deprecated early_stopping_rounds parameter with EarlyStopping callback
- Extract early_stopping_rounds from model parameters using pop() before instantiation
- Configure callback with metric_name='rmse', data_name='validation_0', save_best=True
- Reorganize LightGBM callback initialization for improved code readability
- Maintains backward compatibility with eval_set validation approach
- Ensures compatibility with XGBoost 3.1.2+ API requirements