Load entrypoint plugins before builtin and contrib.

[markreidvfx]

This pull request is meant to assist the moving contrib adapters to external repos.
You can use $OTIO_PLUGIN_MANIFEST_PATH to override a contrib adapter, however this can be inflexible and difficult to test your adapter when you install it.
Being able to use a stock install of OTIO also means you don't have to manage pull requests for 2 repos at the same time when starting to move a contrib adapter.

This issue has been mentioned in #1348

[codecov-commenter]

Codecov Report

Merging #1389 (7e513ec) into main (bb49bed) will increase coverage by 0.00%.
The diff coverage is 79.16%.

@@           Coverage Diff           @@
##             main    #1389   +/-   ##
=======================================
  Coverage   86.27%   86.27%           
=======================================
  Files         196      196           
  Lines       19871    19883   +12     
  Branches     2309     2312    +3     
=======================================
+ Hits        17144    17155   +11     
  Misses       2161     2161           
- Partials      566      567    +1     

Flag	Coverage Δ
py-unittests	86.27% <79.16%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
...-opentimelineio/opentimelineio/plugins/manifest.py	86.56% <66.66%> (ø)
tests/test_plugin_detection.py	82.95% <91.66%> (+1.37%)	⬆️

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[reinecke]

This looks good! One question, is there a way we could add a unittest to check the precedence? This file seems to have a lot of tests around this sort of thing.

If the unittesting gets a bit too difficult or hacky to implement, I think we can just call it a CBB since we already weren't testing it.

[markreidvfx]

I'll take a look, I think I can use part of those existing tests and come up with something that isn't too hacky.

[markreidvfx]

I added a unit test, please take a look when you have the time

[jminor]

@ssteinbach does this conflict with the downgrader PR at all? Do you care if this lands before/after that one?

[reinecke]

Great! Thanks for adding the test!

[ssteinbach]

@ssteinbach does this conflict with the downgrader PR at all? Do you care if this lands before/after that one?

Not an issue. The only file in common is in manifest.py and it isn't a conflicting change. Go for it!

[ssteinbach]

@jminor do you want to land this before or after the next release? (IE do you want to land it at the beginning of the next cycle or at the end of this one)

[markreidvfx]

It would be especially helpful for people working on extracting contrib adapters if it was in the next wheel release. 🙂 It would allow running unit test against a wheel, at least for me, instead of having to compile OTIO everytime i run CI. saves a lot time/cycles.