feat: pass flag_metadata from resolution to evaluation details

[federicobond]

This PR

Implements Requirement 1.4.14

If the flag metadata field in the flag resolution structure returned by the configured provider is set, the evaluation details structure's flag metadata field MUST contain that value. Otherwise, it MUST contain an empty record.

[codecov]

Codecov Report

Merging #212 (0dab979) into main (d41cea2) will increase coverage by 0.27%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #212      +/-   ##
==========================================
+ Coverage   92.93%   93.21%   +0.27%     
==========================================
  Files          16       16              
  Lines         439      442       +3     
==========================================
+ Hits          408      412       +4     
+ Misses         31       30       -1     

Flag	Coverage Δ
unittests	93.21% <100.00%> (+0.27%)	⬆️

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

Files	Coverage Δ
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%)	⬆️

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