Make Paganin processor work with one angle

[hrobarts]

Changes

Make PaganinProcessor work if there is just one angle in the AcquisitionData

Testing you performed

Please add any demo scripts to https://github.com/TomographicImaging/CIL-Demos/tree/main/misc
Added test case in test_DataProcessor.py

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
• Change pull request label to 'Waiting for review'

Contribution Notes

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• 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
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[gfardell]

I feel like this has grown in complexity. I would try to avoid using DataContainer.fill, and instead look at dealing directly with the array i.e. numpy.copyto or equivalent. That means this whole block would condense in to one command.

You already have i and j defined so you should be able to access the array and copy the relevant portions in directly. You could either calculate the start and end indices of your data block, or reshape the array keeping singleton dimensions in.

If the data isn't in a defined order (maybe that's why you're using fill?) there's a strong argument to reorder it first as writing the memory back to the block will be significantly faster if it's a contiguous block you're writing out.