Add FwBlktVVShape enum and update blanket shape checks in models

[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.

[Copilot]

Pull request overview

This PR introduces a typed enum to represent first-wall/blanket/vacuum-vessel shape options and updates several model shape-selection checks to use that enum instead of a raw numeric literal, improving readability and reducing “magic number” usage across geometry-related models.

Changes:

• Added FwBlktVVShape (IntEnum) to represent i_fw_blkt_vv_shape options.
• Replaced fwbs_variables.i_fw_blkt_vv_shape == 1 checks with == FwBlktVVShape.D_SHAPED in multiple models.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
process/models/build.py	Adds the FwBlktVVShape enum definition.
process/models/vacuum.py	Updates vacuum vessel shape branching to use the enum constant.
process/models/shield.py	Updates shield shape branching to use the enum constant.
process/models/fw.py	Updates first wall shape branching to use the enum constant.
process/models/blankets/blanket_library.py	Updates blanket geometry branching to use the enum constant in two locations.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 61.53846% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.05%. Comparing base (09c52f5) to head (44a6b77).

Files with missing lines	Patch %	Lines
process/models/blankets/blanket_library.py	33.33%	2 Missing ⚠️
process/models/fw.py	50.00%	1 Missing ⚠️
process/models/shield.py	50.00%	1 Missing ⚠️
process/models/vacuum.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4167      +/-   ##
==========================================
+ Coverage   48.04%   48.05%   +0.01%     
==========================================
  Files         144      144              
  Lines       30211    30219       +8     
==========================================
+ Hits        14515    14523       +8     
  Misses      15696    15696              

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