Nested Hybrid Grid: prototype improved parent-child result (FIPNEST) through INIT file

[kriben]

The current solution uses sidecar files result (OLDIJK/NEWIJK) which is used to determine the nested hybrid grid LGRs (NHG).

It would be preferable with a simpler result that was part of the INIT file. Suggested result name is FIPNEST.

Three things needs to be implemented to test this:

• Export the "child-to-immediate parent index" for the whole nested hybrid grid as a GRDECL file.
• Use a python library to insert the FIPNEST into an existing INIT file. https://github.com/equinor/resfo/ should work?
• Add a NHG import path which detects the presence of FIPNEST, and creates a NHG based on it without using OLDIJK/NEWIJK side car. A grid imported with the sidecar and a grid imported with the FIPNEST property should be equal.