Add dimensionless current drive eff

[chris-ashe]

This pull request introduces the calculation, storage, and output of the dimensionless current drive efficiency (ζ) for both primary and secondary heating and current drive (HCD) systems. Additionally, a unit test for the new calculation is included.

$$ \zeta = \frac{e^3}{\epsilon^2}\frac{n_e R_0}{T_e}\frac{I_{\text{HCD}}}{P_{\text{HCD}}} $$

Current Drive Efficiency Enhancements:

• Added calculation of the dimensionless current drive efficiency (ζ) for both primary and secondary HCD systems in CurrentDrive.cudriv, using a new method calculate_dimensionless_current_drive_efficiency. The results are stored in eta_cd_dimensionless_hcd_primary and eta_cd_dimensionless_hcd_secondary.
• Updated the output routines to write the new ζ values for both primary and secondary systems to the output file. [1] [2]
• Extended the data structure in current_drive_variables.py to include new fields for storing ζ values, and initialized them appropriately.
• Updated the plasma information plot to display ζ alongside other current drive efficiency metrics for both primary and secondary systems.

🎨 Output

Testing:

• Added a unit test for calculate_dimensionless_current_drive_efficiency to verify its correctness for a simple case.## 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 76.92308% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.10%. Comparing base (b143420) to head (37a265c).

Files with missing lines	Patch %	Lines
process/current_drive.py	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3985      +/-   ##
==========================================
+ Coverage   46.09%   46.10%   +0.01%     
==========================================
  Files         123      123              
  Lines       28888    28901      +13     
==========================================
+ Hits        13316    13326      +10     
- Misses      15572    15575       +3     

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[j-a-foster]

Happy with changes.