Implement hub callback priorities (#2530)

* Implement hub callback priorities
* Update glue/core/hub.py
* Address review comments
* Move yield loop out of subscriber loop
* Add test
* Update docstrings
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Co-authored-by: Derek Homeier <[email protected]>
Co-authored-by: Thomas Robitaille <[email protected]>

Merge pull request #2502 from astrofrog/update-hashes

Update figure hashes

Merge pull request #2486 from astrofrog/fix-profile-ylimits-units

Fix bug that caused IncompatibleAttribute error when trying to change limits

Merge pull request #2482 from bmorris3/transparent-out-of-bounds

Allow transparent regions in composite images when out of bounds

Merge pull request #2484 from astrofrog/unit-conversion-fixes

Fix bugs with attribute display units

Merge pull request #2475 from Carifio24/serialize-units

Allow serializing and deserializing named astropy units

Merge pull request #2477 from astrofrog/remove-deprecated-qt

Remove deprecated Qt-related code

Merge pull request #2465 from jfoster17/improve-region-axis-checking

Provide stronger checking for region display. Fix x/y flip.

Merge pull request #2453 from astrofrog/custom-stretches-instances

Make stretches be customizable on a layer by layer basis

Merge pull request #2455 from astrofrog/customizable-limits-percentile

Customizable limits percentile and behavior on updating bins when resetting limits