Add radiation loss function plot

[chris-ashe]

This pull request refactors and extends the impurity radiation profile plotting functionality in process/core/io/plot/summary.py. The main changes include renaming and updating the radiation profile plotting function for clarity and consistency, adding a new function to plot the line and bremsstrahlung loss function profile, and updating the summary plotting page to use these new functions and improve subplot arrangement.

Plotting function improvements:

• Renamed and refactored plot_radprofile to plot_line_bhrem_power_density_profile, updating its API to use a more descriptive name and clearer parameter types, and switching from the prof argument to axis for consistency with matplotlib conventions.
• Added a new function plot_line_bhrem_loss_function_profile to plot the line and bremsstrahlung loss function ($L_z$) profiles, including log-log interpolation and improved axis labeling.

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 2.29885% with 85 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.64%. Comparing base (78d50cc) to head (d39c580).

Files with missing lines	Patch %	Lines
process/core/io/plot/summary.py	2.29%	85 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4488      +/-   ##
==========================================
- Coverage   48.73%   48.64%   -0.09%     
==========================================
  Files         151      151              
  Lines       29766    29822      +56     
==========================================
+ Hits        14505    14506       +1     
- Misses      15261    15316      +55     

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