Add confinement mode enum

[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 92.40506% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.82%. Comparing base (bcd37bc) to head (2a7ef9f).

Files with missing lines	Patch %	Lines
process/models/physics/confinement_time.py	16.66%	5 Missing ⚠️
process/core/init.py	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4401      +/-   ##
==========================================
+ Coverage   48.80%   48.82%   +0.02%     
==========================================
  Files         151      151              
  Lines       29348    29364      +16     
==========================================
+ Hits        14323    14338      +15     
- Misses      15025    15026       +1     

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