Add bruner div heat split

[chris-ashe]

Description

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 36.73469% with 217 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.13%. Comparing base (b9b6a45) to head (531e765).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
process/models/tfcoil/superconducting.py	24.68%	119 Missing ⚠️
process/models/physics/exhaust.py	34.48%	38 Missing ⚠️
process/core/io/plot/summary.py	7.40%	25 Missing ⚠️
process/models/physics/physics.py	0.00%	16 Missing ⚠️
process/models/physics/scrape_off_layer.py	5.88%	16 Missing ⚠️
process/core/init.py	0.00%	1 Missing ⚠️
process/models/build.py	0.00%	1 Missing ⚠️
process/models/superconductors.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4511      +/-   ##
==========================================
- Coverage   49.14%   49.13%   -0.01%     
==========================================
  Files         152      152              
  Lines       29803    29918     +115     
==========================================
+ Hits        14647    14701      +54     
- Misses      15156    15217      +61     

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