Add CS Tresca and 2D contour plots

[chris-ashe]

This pull request makes significant improvements to the central solenoid (CS) stress modeling, variable naming consistency, and documentation. The main changes include refactoring variable names for clarity, adding new stress calculation methods (Tresca and von Mises), expanding the CS stress data model, and updating documentation to match the new, more general approach to CS stress calculations.

Central Solenoid Stress Modeling and Calculations:

• Added new functions for calculating Tresca (maximum shear) and von Mises stresses to materials.py, enabling more comprehensive CS stress analysis.
• Expanded the PFCoilData class to include vertical profiles of axial stress, radial stress (peak and inner), and von Mises stress for the central solenoid.
• Updated the CS stress output to use new variable names and removed the i_cs_stress switch, reflecting a shift to always considering both hoop and axial stresses.

Variable Naming Consistency and Refactoring:

• Renamed the variable alstroh to stress_cs_steel_max throughout the codebase, input files, and documentation for clarity and consistency.
• Updated obsolete variable mapping to reflect the renaming and to ensure backward compatibility.

Documentation Updates:

• Overhauled the central solenoid stress documentation to provide a more general axial stress formula, clarify the meaning of variables, and add a new section for peak axial stress.
• Removed outdated explanations and references to the old i_cs_stress switch and clarified the use of Tresca and von Mises criteria.

These changes modernize the CS stress model, improve clarity for users and developers, and lay the groundwork for more advanced stress analysis and postprocessing.

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 17.21854% with 250 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.53%. Comparing base (23787f8) to head (aa63297).

Files with missing lines	Patch %	Lines
process/core/io/plot/summary.py	3.54%	245 Missing ⚠️
process/models/pfcoil.py	83.87%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4325      +/-   ##
==========================================
- Coverage   48.77%   48.53%   -0.25%     
==========================================
  Files         151      151              
  Lines       29390    29643     +253     
==========================================
+ Hits        14336    14386      +50     
- Misses      15054    15257     +203     

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