🐛 Fix stacked plots functionality by ensuring multiple output var…

[chris-ashe]

This pull request refactors the logic for handling stacked plots in the main function of process/io/plot_scans.py. The main improvement is to ensure that subplots for stacked plots are created only once, and only when needed, thereby fixing potential issues with subplot creation and improving code clarity.

Plotting logic improvements:

• Moved the creation of subplots for stacked plots (fig, axs = plt.subplots(...)) from the outer loop to occur only once, at the first relevant iteration, preventing redundant subplot creation and related errors.
• Removed the previous subplot creation block from the outer loop and replaced it with a pass statement, since subplot creation is now handled inside the plotting logic.
• Added a check to raise a ValueError if stacked plots are requested with only one output variable, ensuring proper usage and error handling.…iables are handled correctly

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 0% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 46.56%. Comparing base (e06c522) to head (c980191).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
process/io/plot_scans.py	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4068      +/-   ##
==========================================
- Coverage   46.60%   46.56%   -0.05%     
==========================================
  Files         122      124       +2     
  Lines       28711    28981     +270     
==========================================
+ Hits        13381    13495     +114     
- Misses      15330    15486     +156     

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[timothy-nunn]

Can you give me an example of the bug this fixes please (an MFile + commands to run)... its not immediately obvious what the problem was and how this fixes it.

[timothy-nunn]

Please rewrite this if statement to avoid just having a pass