Permeability class obsolete
The permeability class seems not to be used in the code anymore. Both the initialization and rendering of output is handled by the Porv_poro_trans class (docstring needs updating). Can it simply be removed?
https://github.com/equinor/flownet/blob/master/src/flownet/parameters/_permeability.py https://github.com/equinor/flownet/blob/master/src/flownet/parameters/_porv_poro_trans.py
Permeability is not part of the pickled parameters:

Seems like a good idea.
Looking at https://github.com/equinor/flownet/blob/6eb0fd57d1a328567a46b68b0afdf17aa6117f56/src/flownet/parameters/_porv_poro_trans.py#L124-L132
suggests that the PERM is not rendered there, but it actually is.