4183 improve the representation of neutral beam tangency in the toroidal cross section plotting

[grmtrkngtn]

Description

Revamps beam tangency plotting, fixes a few geometry accounting errors.
Fix NBI duct plotting by using shielded TF width and constructing the beam edges and centreline consistently from tangent geometry.
This ensures the duct is symmetric about the true beam centreline and aligns with the PROCESS docs.

• Adds a centre-line to beam duct plotting.

result:

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 0% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.06%. Comparing base (4c99916) to head (82b7056).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
process/core/io/plot/summary.py	0.00%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4199      +/-   ##
==========================================
- Coverage   52.07%   52.06%   -0.02%     
==========================================
  Files         148      148              
  Lines       30321    30324       +3     
==========================================
- Hits        15791    15789       -2     
- Misses      14530    14535       +5     

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