Aggregated simulation results lost attributes #342
Description
In protocol.calc_solution, when the simulation_result_aggregated Dataset is created, it's arrays are found by collapsing multiple foci into a single, aggregated result. However, xa.Datarray.max does not by default keep the attributes of the DataArray, which results in losing the units attribute. This causes the aggregated result to no longer have rescaleable units via util.units.rescale_data_arr.