Add stored thermal energy calcs

[chris-ashe]

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 50.00000% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.81%. Comparing base (e24884c) to head (9ae0d39).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
process/models/physics/physics.py	26.31%	14 Missing ⚠️
process/models/physics/confinement_time.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4399      +/-   ##
==========================================
- Coverage   48.84%   48.81%   -0.04%     
==========================================
  Files         151      151              
  Lines       29377    29379       +2     
==========================================
- Hits        14348    14340       -8     
- Misses      15029    15039      +10     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.