consistency
E.g. tl.kmf operates on two arrays (see also #387) while tl.nelson_aalen operates on an anndata.
The latter should be the norm here if suitable.
passing all required arguments
Then, e.g. tl.weibull doesnt take the entry column or any way to pass this to the fitter; harmonizing this to ensure all flexibility offered by lifelines is userfacing would be a great enhancement!
Description of feature