Image Geometry get_slice returns IG with offset centre

[lauramurgatroyd]

Description

Closes #2217

• Adds get_centre_slice method to ImageData, ImageGeometry, AcquisitionGeometry
• Allows passing vertical='centre' to ImageGeometry.get_slice
• Sets center_x, center_y, center_z appropriately for ImageGeometry returned by get_slice

Example Usage

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

Changes

Testing you performed

Please add any demo scripts to https://github.com/TomographicImaging/CIL-Demos/tree/main/misc

Added unit tests for:

• Image Geometry get_slice
• New get_centre_slice methods

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

[hrobarts]

Hi Laura, this looks really useful. Just a couple of questions.