docs: def _dqdv_combinded_frame(cell, **kwargs):
      """Returns full cycle dqdv data for all cycles as one pd.DataFrame.
  
          Args:
              cell: CellpyData-object
  
          Returns:
              pandas.DataFrame with the following columns:
                  cycle: cycle number
                  voltage: voltage
                  dq: the incremental capacity
      """
  
      cycles = cell.get_cap(
          method="forth-and-forth",
          categorical_column=True,
          label_cycle_number=True,
      )
      ica_df = dqdv_cycles(cycles, **kwargs)
      assert isinstance(ica_df, pd.DataFrame)
      return ica_df