The data_fraction column in forward_backward_convergence will be scaled by the unit converter in ABFE workflow

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In the ABFE workflow, the convergence dataframe is passed into the unit converter to ensure that it outputs the correct unit, which will convert data_fraction column as well. For example, if the output is kcal/mol, the data_fraction column which is for example [0.0, 0.1, 0.2, ..., 1.0] will be converted to [0.061, 0.123, 0.184, ..., 0.616].