feat: implement provider status

[federicobond]

This self-contained change introduces the functionality required to properly implement provider status events later. It has no user-visible changes at this point.

I wanted to split this out of the events pull request because it had the potential to snowball the size of the diff and lower the quality of the review in general.

I've introduced several seams that will make it easy to attach event handlers that respond to status changes later on.

[codecov]

Codecov Report

Attention: Patch coverage is 89.28571% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 94.06%. Comparing base (7ba7d61) to head (81cf99c).

Files	Patch %	Lines
openfeature/provider/registry.py	80.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #288      +/-   ##
==========================================
- Coverage   94.71%   94.06%   -0.66%     
==========================================
  Files          18       18              
  Lines         492      539      +47     
==========================================
+ Hits          466      507      +41     
- Misses         26       32       +6     

Flag	Coverage Δ
unittests	94.06% <89.28%> (-0.66%)	⬇️

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[toddbaert]

The "short circuiting" behavior mentioned in 1.7.6 and 1.7.7 might be relevant enough to implement here as well: https://github.com/open-feature/spec/blob/37cf68b0d68b6814514bcded521b9e199efcead3/specification/sections/01-flag-evaluation.md?plain=1#L485-L502

[toddbaert]

Nothing looks wrong here to me, but there's a few related things that might be worth adding.

[toddbaert]

This looks fully spec compliant to me, as far as provider status stuff goes.

[gruebel]

nice work 🏅