Add option for loop voltage fudge factor

[jonmaddock]

In GitLab by @ajpearcey on Jun 19, 2023, 11:29

To help the loop voltage calculate agree with other transport code we should add in a user set coefficient.

[mkovari]

Hazardous but probably necessary.

[jmorris-uk]

There is a plasma resistivity factor in the code that was used to match PLASMOD in the past. Would probably be worth reviewing that in combination with the loop voltage.

[mkovari]

We shouldn't be adding in fudge factors without warning the users.

It would be good to have a better physics-based 0D formula for plasma resistivity if we can find one. The formula we are using is from the 1980s.