Function merge_dataframes_on_with 

pub fn merge_dataframes_on_with(
    left: &DataFrame,
    right: &DataFrame,
    left_on: &[&str],
    right_on: &[&str],
    join_type: JoinType,
) -> Result<MergedDataFrame, JoinError>

Merge two DataFrames on one or more key columns.

Matches pd.merge(left, right, left_on=left_keys, right_on=right_keys, how=join_type).

• Key columns are used for matching rows (hash join).
• Non-key columns are carried through and reindexed.
• Column name conflicts use configurable suffixes (default _x/_y).
• The output index is auto-generated (0..n RangeIndex-style).