Fix #220: accept list/array X_row across explainer methods

[oegedijk]

Summary

• add shared X_row normalization for list/tuple/ndarray single-row inputs
• support list/array X_row in get_contrib_df and related APIs (get_col_value_plus_prediction, pdp_df, classifier/regression prediction_result_df)
• update docstrings, TODO, and release notes
• add regression tests for classifier and regression paths

Testing

• uv run pytest tests/test_classifier_base.py -k "contrib_df_accepts_list_or_array_X_row or prediction_result_df_accepts_list_or_array_X_row or pdp_df_accepts_list_or_array_X_row or get_col_value_plus_prediction_accepts_list_or_array_X_row" -q
• uv run pytest tests/test_regression_base.py -k "prediction_result_df_accepts_list_or_array_X_row or pdp_df_accepts_list_or_array_X_row or get_col_value_plus_prediction_accepts_list_or_array_X_row" -q

Closes #220