Fix nbi power: correct shine-through, use plasma-coupled power instead of raw power; corrected wall-plug power conversion

[grmtrkngtn]

Description

• We were applying f_p_beam_shine_through incorrectly in two ways:
  • f_p_beam_shine_through represents the fraction of beam power that is not absorbed, but we were using (1 - f_p_beam_shine_through)
  • the fraction was only being applied to part of the power term due to operator precedence, rather than the total beam power
• Fixed ion/electron power split:
  • previously based on injected beam power
  • now correctly based on plasma-coupled beam power
• Fixed wall-plug power calculation (pwpnb):
  • previously only part of the power term was divided by injector efficiency
  • now the full beam power term is divided by efficiency

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 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 49.61%. Comparing base (dfaa47b) to head (aa6f098).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
process/models/physics/physics.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4187      +/-   ##
==========================================
- Coverage   49.61%   49.61%   -0.01%     
==========================================
  Files         148      148              
  Lines       29753    29751       -2     
==========================================
- Hits        14762    14760       -2     
  Misses      14991    14991              

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