Minor refactoring of polarization values and defaults in the slicer function

[confluence]

Description

This is a set of refactoring changes:

• Removing redundant lookups of integers with same integer enums
• Using correct protobuf function to cast integers to integer enums
• General cleanup of polarization values (descriptions; CASA and FITS conversion...)
• Replacing unnecessarily complex and inefficient ordering of small unordered maps with polarization keys (these can just be ordered maps)
• Precalculating fixed ranges for full X, Y and Z and using the X and Y ranges as defaults to GetImageSlicer instead of using a placeholder default which has to be checked and possibly replaced whenever the function is called
• Reimplementing functions for mapping polarization index to polarization value and vice versa

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

[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	37%	❌
Summary	46% (8634 / 18964)	➖

[pford]

I did not realize the protobuf enums had these built-in functions. We should check if this can be used in other refactoring!

[kswang1029]

all e2e tests are passing. regular Stokes cubes are fine (including hypercubes). rotated cubes are fine in switching IQUV (will crash if switching computed components).