Add Redl model of bootstrap current

[theo-brown]

Part of ongoing JETTO validation. JETTO/NCLASS shows close agreementh with Redl 2021, but worse agreement with Sauter 1999. Updating the bootstrap current to the Redl model (as noted in the comment) would improve quality of JETTO/TORAX comparisons, particularly in large bootstrap regimes (eg ST).

torax/torax/_src/neoclassical/bootstrap_current/sauter.py

Line 112 in 0941209

# Formulas from Sauter PoP 1999. Future work can include Redl PoP 2021

[Thakor-Yashpal]

Hi, I see this issue to add the Redl bootstrap current model is still open and unassigned. I have an interest in this area and would like to work on implementing it and submitting a pull request. Please let me know if I can take this on.

[jcitrin]

Thank you for your intererst in contributing. However this issue would be best tackled by someone with some tokamak simulation domain experience, even if AI-assisted. If this is not the case then I do not recommend taking it on.