BlocksOnCylindrical refactor and add axial bucket gaps

[robbietuk]

Attempts to address some issues found with GeometryBlocksOnCylindrical, as detailed here https://github.com/UCL/STIR/discussions/1388, and add gaps between buckets.

Changes in this pull request

• Refactor of GeometryBlocksOnCylindrical. Significant change to the calculations of build_crystal_maps.
• Refactor of Scanner. This added a number of simplifications to the way the get_* methods work around buckets/block/crystal gaps and numbers

Testing performed

• Additional testing for GeometryBlocksOnCylindricalTests.

Related issues

Checklist before requesting a review

• [] I have performed a self-review of my code
• [] I have added docstrings/doxygen in line with the guidance in the developer guide
• [] I have implemented unit tests that cover any new or modified functionality (if applicable)
• [] The code builds and runs on my machine
• [] documentation/release_XXX.md has been updated with any functionality change (if applicable)

[robbietuk]

Currently, a number of tests are failing, I might have broken something with symmetries etc...

[KrisThielemans]

@markus-jehl this one might be somewhat relevant to your problem.