refactor!: rename top-level package to openfeature

[federicobond]

This PR

Renames the top-level package from open_feature to openfeature.

Related Issues

#181

[codecov]

Codecov Report

Merging #192 (6c5e434) into main (25f6a87) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #192   +/-   ##
=======================================
  Coverage   92.93%   92.93%           
=======================================
  Files          16       16           
  Lines         439      439           
=======================================
  Hits          408      408           
  Misses         31       31           

Flag	Coverage Δ
unittests	92.93% <100.00%> (ø)

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Files Changed	Coverage Δ
openfeature/_backports/strenum.py	100.00% <ø> (ø)
openfeature/evaluation_context.py	90.90% <ø> (ø)
openfeature/exception.py	84.37% <ø> (ø)
openfeature/immutable_dict/mapping_proxy_type.py	83.33% <ø> (ø)
openfeature/provider/metadata.py	100.00% <ø> (ø)
openfeature/api.py	100.00% <100.00%> (ø)
openfeature/client.py	95.60% <100.00%> (ø)
openfeature/flag_evaluation.py	97.72% <100.00%> (ø)
openfeature/hook/__init__.py	86.11% <100.00%> (ø)
openfeature/hook/hook_support.py	86.48% <100.00%> (ø)
... and 6 more

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