add mode for RC correlation based on segments

[AcKoucher]

This should resolve the first item on #3969.

For now, I'm adding the segment-based regression as an additional mode rather than replacing net-based. The idea is to let the new mode stabilize.

Observations

1. Net-based approach used parasitics data from STA (loaded with read_spef). On the other hand, segment-based needs the parasitics of each routing shape in ODB and, as 6_final.odb does not contain parasitics data, we need to extract_parasitics before trying to retrieve the required data from ODB.
2. The parasitcs extraction needs to be made in such a way that the wire shapes correctly match the resistive segments (see the arguments used when calling extract_parasitics).
3. Note that I also used segment-based for resistance. The reason is: even though it's not necessary, it would be more confusing to have a hybrid approach to generate set_layer_rc values i.e., net-based for resistance and segment-based for capacitance. In segment-based, it is also easier to process the resistance of the .csv file as we don't need to manually decrease the vias' resistance of each net.