[BUG] timeindex_worst_cases is not saved

[khelfen]

Describe the bug
When saving a worst-case edisgo object the timeindex_worst_cases attribute should be saved as well as it gives an error when trying to do calculations with the worst-case time series but with missing timeindex_worst_cases.

Expected behavior
timeindex_worst_cases should be saved when running edisgo.save()

eDisGo/edisgo/network/timeseries.py

Line 1875 in d36d114

def to_csv(self, directory, reduce_memory=False, time_series_raw=False, **kwargs):