Fix bug with show2D not rendering with single plot

[lauramurgatroyd]

Description

Fixes #2326
show2D wasn't working with a single plot because plt.subplots was not returning an array in that case.
Updated to use squeeze=False kwarg to ensure an array is always returned: https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.subplots.html

Also updated to:

• Delete the 'extra' axes instead of hiding them
• Make use of .flat instead of .flatten()

Example Usage

Running https://github.com/TomographicImaging/CIL-Demos/blob/main/demos/1_Introduction/03_preprocessing.ipynb

Contribution Notes

• The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in CIL (the Work) under the terms and conditions of the Apache-2.0 License
• I confirm that the contribution does not violate any intellectual property rights of third parties

Testing you performed

Note: no unit tests cover this
Run https://github.com/TomographicImaging/CIL-Demos/blob/main/demos/1_Introduction/03_preprocessing.ipynb
to test show2D behaviour with different numbers of plots

Also edited one of the prints to make sure it still worked when we had figures across multiple rows where one row is incomplete e.g.

Compared behaviour to v25.0.0 and made sure it matched it

Related issues/links

Checklist

• I have performed a self-review of my code
• I have added docstrings in line with the guidance in the developer guide
• I have updated the relevant documentation
• I have implemented unit tests that cover any new or modified functionality
• CHANGELOG.md has been updated with any functionality change
• Request review from all relevant developers

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[gfardell]

great!

[lauramurgatroyd]

Note: only failure is expected docker failure currently on master