Inconsistent treatment of solenoid current

We have both solenoid current and voltages in the dataset. However, they are treated differently. We have:

- `pf_active/solenoid_current` for the current
- But the solenoid voltage is the first record in the `pf_active/coil_voltage`

I think it should be one way or the other. We should look to the IMAS schema for guidence...