Aggregate information about image axes and dimensions into structs

[confluence]

Description

This is a refactoring PR which aggregates information about image axes and dimensions into two structs. This simplifies passing the information around and storing it as properties: we can use the structs instead of inconsistent subsets of individual axes and dimensions.

Major changes:

• FileLoader::::FindCoordinateAxes signature has changed; it now only sets _axes and _dims on the loader and does not also modify return parameters (but it's still a bool and may set the message parameter).
• Individual axes properties in FileLoader and Frame replaced with structs. Individual getters have been kept; getters for the structs have been added.
• Calculation of dims from axes and shape moved to dims struct constructor to enable cleaner reuse from multiple places where axes can be calculated.
• Frame, HDF5 loader, polarization calculator, Stokes file connector, extended file info loader updated to use axes and/or dims structs.

There are two non-refactoring changes:

1. While I was making this change I noticed that previously the spectral axis of a compressed FITS file was being set to the depth axis, and have fixed this. At the moment compressed FITS files with rotated axes can't be viewed at all for unrelated reasons; I will see how easy that would be to fix, and possibly factor these changes out into a separate PR.
2. FileLoader::::FindCoordinateAxes now explicitly bails out with an error message if there are fewer than 2 render axes (e.g. in a weird case like a 2D image with one Stokes axis). Previously I believe that this would have crashed. Maybe we should give images like this a second render axis with size 1 (like we handle images with no depth or Stokes), but that would be a much more complicated change (and it may not be something we need).

Possible outstanding issue

• There are hardcoded axes in Frame's image export functions. Should these be updated to support rotated axes?

Checklist

• changelog updated / no changelog update needed
• e2e test passing / corresponding fix added / new e2e test created
• ICD test passing / corresponding fix added / new ICD test created
• protobuf updated to the latest dev commit / no protobuf update needed
• protobuf version bumped / protobuf version not bumped
• added reviewers and assignee
• GitHub Project estimate added

[pford]

Remove spectral and stokes axis from CompressedFits

[pford]

I could not find anything that was missed.
I can fix the Save Image bug for issue #1178 (additional support for rotated cubes).

[github-actions]

Package	Line Rate	Health
src.Cache	72%	➖
src.DataStream	44%	➖
src.FileList	67%	➖
src.Frame	35%	❌
src.HttpServer	42%	➖
src.ImageData	28%	❌
src.ImageFitter	83%	✔
src.ImageGenerators	43%	➖
src.ImageStats	75%	✔
src.Logger	37%	❌
src.Main	52%	➖
src.Region	69%	➖
src.Session	4%	❌
src.Table	52%	➖
src.ThreadingManager	67%	➖
src.Timer	85%	✔
src.Util	38%	➖
Summary	46% (8638 / 18950)	➖

[kswang1029]

Loading individual Stokes images as a hypercube does not work. This is picked up by e2e. Requesting @pford a re-review once addressed.

The test images in the screenshot all have Shape = [256, 256, 480, 1] (RA, DEC, FREQ, STOKES).

Other tests images with Shape = [256, 256, 480] (RA, DEC, FREQ) or Shape = [6280, 3140] (GLON, GLAT) work however.