Inconsistency of .sum() for Fields and Linearizations
Is it wanted that Linearization.sum() returns a scalar Field but Field.sum() returns an actual scalar, i.e. in most situations a float? MultiField.sum() inherits the behaviour from Field.
Linearizations: https://gitlab.mpcdf.mpg.de/ift/nifty/blob/NIFTy_6/nifty6/linearization.py#L237
Fields: https://gitlab.mpcdf.mpg.de/ift/nifty/blob/NIFTy_6/nifty6/field.py#L382
MultiFields: https://gitlab.mpcdf.mpg.de/ift/nifty/blob/NIFTy_6/nifty6/multi_field.py#L169