🏋️ Calculate plasma fuelling masses

[chris-ashe]

This pull request includes significant updates to the process/physics.py and source/fortran/physics_variables.f90 files, focusing on the calculation and output of plasma mass variables. The most important changes include the addition of a new method for calculating plasma masses and the inclusion of these calculations in the output.

Changes in process/physics.py:

• Added a new method calculate_plasma_masses to compute various plasma mass variables, including fuel ions, total ions, alpha particles, electrons, and the total plasma mass.
• Updated the physics method to call calculate_plasma_masses and assign the results to corresponding variables in physics_variables.
• Enhanced the outplas method to include the new plasma mass variables in the output file.

Changes in source/fortran/physics_variables.f90:

• Introduced new variables to store the mass of plasma components in grams: m_plasma_fuel_ions_grams, m_plasma_ions_total_grams, m_plasma_alpha_grams, m_plasma_electron_grams, and m_plasma_grams.
• Initialized the new plasma mass variables in the init_physics_variables subroutine.

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

Attention: Patch coverage is 57.14286% with 6 lines in your changes missing coverage. Please review.

Project coverage is 31.73%. Comparing base (cf82f05) to head (087d51a).
Report is 138 commits behind head on main.

Files with missing lines	Patch %	Lines
process/physics.py	57.14%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3598      +/-   ##
==========================================
+ Coverage   31.71%   31.73%   +0.01%     
==========================================
  Files          84       84              
  Lines       20152    20166      +14     
==========================================
+ Hits         6392     6400       +8     
- Misses      13760    13766       +6     

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