feat: implement provider events

[federicobond]

This PR

• Adds support for eventing according to the spec. Looking for feedback especially on the public API

Follow-up Tasks

• Improve tests
• Run event handlers with a ThreadPoolExecutor

Fixes: #278

[codecov]

Codecov Report

Attention: Patch coverage is 98.16514% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 94.77%. Comparing base (04b4009) to head (d4420f3).

Files	Patch %	Lines
openfeature/_event_support.py	97.50%	1 Missing ⚠️
openfeature/provider/provider.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #278      +/-   ##
==========================================
+ Coverage   94.19%   94.77%   +0.58%     
==========================================
  Files          18       20       +2     
  Lines         551      651     +100     
==========================================
+ Hits          519      617      +98     
- Misses         32       34       +2     

Flag	Coverage Δ
unittests	94.77% <98.16%> (+0.58%)	⬆️

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[toddbaert]

I'll take a close look at this in the next couple days.

[toddbaert]

Please pardon my lack of Python skills if I'm missed something.

Overall the structures and API look great!

I left some requested changes specifically on the finer points of the eventing spec. They can be tricky, and some of it could be better fleshed-out in the spec, as I think you noted before. I will work on some additional supporting explanations today. Thanks for your efforts here! 🙏

[toddbaert]

@federicobond I've opened open-feature/spec#248

[federicobond]

This should be ready to review from a specification perspective, we might want to add some further tests maybe.

[matthewelwell]

@federicobond I've added a few comments here from a python perspective but I don't purport to be an expert so feel free to ignore as you see fit!

[federicobond]

From Requirement 5.1.1:

Providers cannot emit PROVIDER_CONTEXT_CHANGED or PROVIDER_RECONCILING event.

Should we add a guard to make sure this cannot happen?

[matthewelwell]

Apologies for the delay in responding here @federicobond, I really need to look into my GH notifications 🙄

I've added a few more comments in response to yours. Again, I'm happy to be ignored on any of them if you see fit.

[federicobond]

@matthewelwell I refactored the EventSupport implementation so that we are no longer using private module imports. It should be much cleaner now.

[gruebel]

great work, just few minor comments/questions

[matthewelwell]

Looks good, thanks @federicobond !

All issues resolved.

[federicobond]

Merged! 🎉 Thanks everyone for your helpful comments and suggestions.

[beeme1mr]

Amazing, nice job @federicobond!