Add tf inside cs 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 52.94118% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.79%. Comparing base (ae77429) to head (a39155f).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
process/models/build.py	10.00%	9 Missing ⚠️
process/core/io/plot/summary.py	25.00%	3 Missing ⚠️
process/models/tfcoil/base.py	25.00%	3 Missing ⚠️
process/data_structure/build_variables.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4362   +/-   ##
=======================================
  Coverage   48.79%   48.79%           
=======================================
  Files         151      151           
  Lines       29383    29408   +25     
=======================================
+ Hits        14337    14351   +14     
- Misses      15046    15057   +11     

☔ 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.

[clmould]

Just 1 thing but everything else good:

In test_tfcoil.py there are some instances of i_tf_inside_cs=0 - could these be updated to use the enum value instead please?