Scan improvements

[je-cook]

Description

This is part of #4308 but starting to split out things that can be reviewed now.
This removes a lot of duplication around scans.

Also there scan variable 14 was not accessible before (i have made it so here). Is that wanted?

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 34.75936% with 244 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.28%. Comparing base (83d9f63) to head (33d2db5).

Files with missing lines	Patch %	Lines
process/core/io/plot/scans.py	12.50%	203 Missing ⚠️
process/core/scan.py	70.92%	41 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4482      +/-   ##
==========================================
+ Coverage   48.67%   49.28%   +0.61%     
==========================================
  Files         151      151              
  Lines       29734    29467     -267     
==========================================
+ Hits        14474    14524      +50     
+ Misses      15260    14943     -317     

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