- Remove split_at_end parameter from pipeline.transform(), always return DataFrame
- Add pack_struct parameter to pack feature groups into struct columns
- Rename exporters: select_feature_groups_from_df -> get_groups, select_feature_groups -> get_groups_from_fg
- Add pack_structs() and unpack_struct() helper functions
- Remove split_from_merged() method from FeatureGroups (no longer needed)
- Rename dump_polars_dataset.py to dump_features.py with --pack-struct flag
- Update README with new CLI usage and struct column documentation
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
