Update ODL hold calculation logic (PP-1728)

[jonathangreen]

Description

Completely re-work how we are calculating the hold queue for OPDS2 + ODL items.

All the work to calculate the holds is moved out to live in a Celery task. When a hold is invoked through the API the hold is always placed in the queue, and the queue is later recalculated by the celery task.

Motivation and Context

Previously the holds calculation was based on the number of loans that this CM had for an item. This is a problem is a loan gets lost, or if the collection is added to multiple CM. Now we use the number of licenses available, which should be safer and less error prone. However it may still be incorrect if the collection is on multiple CM, as these CM will be fighting for the same hold.

How Has This Been Tested?

• Did some minor local testing
• Unit tests

Checklist

• I have updated the documentation accordingly.
• All new and existing tests passed.

[codecov]

Codecov Report

Attention: Patch coverage is 98.43750% with 3 lines in your changes missing coverage. Please review.

Project coverage is 90.72%. Comparing base (7d44fa4) to head (ea6f173).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/palace/manager/api/odl/api.py	93.33%	1 Missing and 1 partial ⚠️
src/palace/manager/celery/tasks/opds_odl.py	98.95%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2117   +/-   ##
=======================================
  Coverage   90.72%   90.72%           
=======================================
  Files         351      351           
  Lines       40878    40886    +8     
  Branches     8853     8871   +18     
=======================================
+ Hits        37085    37093    +8     
  Misses       2486     2486           
  Partials     1307     1307           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[dbernstein]

Whoa: big PR. Looks good to the extent that I fully grocked it. Way to move another task out of the scripts and into celery.