❇️ ♻️ Create Beta class

[chris-ashe]

This pull request introduces a new PlasmaBeta class to centralize and standardize plasma beta calculations across the codebase. The changes refactor existing code to use this class, update dependencies, and add new unit tests for its methods. The most important changes are grouped below:

Core Refactoring and Architecture:

• Added a new PlasmaBeta class to process.physics and refactored the codebase to use this class for all plasma beta-related calculations, replacing previous standalone functions.

• Updated the initialization of major classes (main.py, stellarator.py) to instantiate and pass PlasmaBeta objects where needed, ensuring consistent access to beta calculations throughout the application.
  Code Cleanup and Removal:

• Removed the now-obsolete fast_alpha_beta function from process/physics_functions.py, migrating its logic to the new PlasmaBeta class.

• Updated all usages of beta calculation functions to use the new class methods, including replacing calls in the Stellarator model.

Testing and Validation:

• Refactored unit tests in test_physics.py and test_stellarator.py to use the new PlasmaBeta class and its methods, ensuring all previous tests remain valid and comprehensive.
• Added new unit tests for additional PlasmaBeta methods, such as calculate_normalised_beta and calculate_plasma_energy_from_beta, to improve coverage and reliability.

Dependency and Import Updates:

• Cleaned up imports in affected files to remove unused beta calculation functions and ensure all references point to the new PlasmaBeta class.

These changes improve maintainability by centralizing plasma beta logic, reduce code duplication, and enhance test coverage.## 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 38.00000% with 93 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.72%. Comparing base (5ea7543) to head (c75741c).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
process/physics.py	37.67%	91 Missing ⚠️
process/main.py	50.00%	1 Missing ⚠️
process/stellarator.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4053      +/-   ##
==========================================
- Coverage   46.49%   45.72%   -0.77%     
==========================================
  Files         123      124       +1     
  Lines       28777    31990    +3213     
==========================================
+ Hits        13381    14629    +1248     
- Misses      15396    17361    +1965     

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[timothy-nunn]

What is the speed impact of no longer JIT compiling this method?

[timothy-nunn]

Can you move the calculations that are not depended on into the new Beta class and add run and output methods to this class.

That way in the caller we can do models.beta.run() (or models.beta.output()) which will run the Beta model (and output if appropriate). Some of the variables will need a bit of untangling (e.g. beta_poloidal_vol_avg which is used later on in physics to calculate f_c_plasma_bootstrap_sakai) but this can be done in a later PR.