♻️ Standardise more blkt code

[chris-ashe]

This pull request introduces improvements to the blanket structure output and plotting, as well as refactors unit tests for blanket half-height calculation. The main enhancements include a new plotting function for the blanket structure that displays both areas and volumes, streamlining of output methods, and simplification of the unit test for blanket half-height by removing unnecessary patching and parameters.

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 41.22449% with 144 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.45%. Comparing base (89a0b72) to head (17b91cf).

Files with missing lines	Patch %	Lines
process/vacuum.py	26.92%	76 Missing ⚠️
process/blanket_library.py	43.39%	30 Missing ⚠️
process/shield.py	72.30%	18 Missing ⚠️
process/io/plot_proc.py	5.88%	16 Missing ⚠️
process/caller.py	0.00%	2 Missing ⚠️
process/main.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4075      +/-   ##
==========================================
- Coverage   46.46%   46.45%   -0.02%     
==========================================
  Files         122      123       +1     
  Lines       28838    28923      +85     
==========================================
+ Hits        13401    13436      +35     
- Misses      15437    15487      +50     

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