spinner while stretch histogram data updating

[kecnry]

Description

This pull request implements a spinner showing when the data for the stretch histogram is updating.

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

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• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8b997fb) 91.52% compared to head (4362f11) 91.52%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2644      +/-   ##
==========================================
- Coverage   91.52%   91.52%   -0.01%     
==========================================
  Files         161      161              
  Lines       19989    19995       +6     
==========================================
+ Hits        18295    18300       +5     
- Misses       1694     1695       +1     

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[pllim]

I think I saw it but I can't be sure. It comes and goes too fast. I saw the histogram blink and what I thought is part of a spinner for a split second.

[camipacifici]

Tested with a very big image and it worked really well. Thank you!

[camipacifici]

And now I broke it... :( I will try to reproduce the problem and see if it is just a glitch or an actual problem.

[camipacifici]

Ok, the problem is with the toggle "limit histogram to current zoom limits". When toggling it, the spinner is just a flash, but the histogram is taking a longer time to settle.

[kecnry]

I think I managed to fix the main issue as well as the flickering spinner sometimes seen for updates that are immediately skipped. Sometimes though the image viewer seems to process its update before the callback is sent to the stretch histogram, resulting in a "delayed" start of the spinner. I'm not sure there is much we can do about these cases. But the spinner should show whenever the histogram itself is processing an update.

Here is what I currently see on my end.

Screen.Recording.2024-01-03.at.3.52.07.PM.mov

[camipacifici]

Works on my end too! Thank you for fixing it.

[gibsongreen]

This is also working for me when data is first loaded and when the zoom is updated and the histogram is limited to said zoom!