Units of historical parameters when cloning

[behnam-zakeri]

When cloning a scenario and shifting the first model year at the same time, e.g., from 2020 to 2025, using shift_first_model_year input argument; the solution of the original scenario for 2020 will be transferred as historical_activity and historical_new_capacity to the cloned scenario. The issue is that the unit of these historical parameters for 2020 will be inserted as ??? in the cloned scenario. It is desirable that Scenario.clone() keeps the units as they are in the original scenario.