feat: implement initialize/shutdown on provider registration

[federicobond]

This PR

Implements initialize/shutdown on provider registration. Covers Requirements 1.1.2.2, 1.1.2.3 and 1.6.1 from the OpenFeature specification.

[codecov]

Codecov Report

Merging #213 (862be1d) into main (d41cea2) will increase coverage by 0.40%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #213      +/-   ##
==========================================
+ Coverage   92.93%   93.34%   +0.40%     
==========================================
  Files          16       16              
  Lines         439      451      +12     
==========================================
+ Hits          408      421      +13     
+ Misses         31       30       -1     

Flag	Coverage Δ
unittests	93.34% <100.00%> (+0.40%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
openfeature/api.py	100.00% <100.00%> (ø)
openfeature/client.py	95.60% <ø> (ø)
openfeature/flag_evaluation.py	97.82% <100.00%> (+0.09%)	⬆️
openfeature/provider/in_memory_provider.py	100.00% <100.00%> (+1.88%)	⬆️
openfeature/provider/provider.py	78.12% <100.00%> (+3.12%)	⬆️

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