CrostonClassic required argument serving no purpose

[nickto]

CrostonClassic has a required argument level:

statsforecast/statsforecast/models.py

Line 3596 in 444f01e

def predict_in_sample(self, level):

However,

1. The method is not implemented, so it does not make sense to make it required.
2. None of the other models have level as a required argument in predict_in_sample() method.

Hence, it seems like it should be either

def predict_in_sample(self, level: Optional[Tuple[int]] = None):

to be consistent with other methods that use level argument.

Or

def predict_in_sample(self):

to be consistent with other not implemented methods.

[kvnkho]

This should be def predict_in_sample(self, level: Optional[Tuple[int]] = None):.

@jaymanalastas, would you like to fix?