refactor!: move api hooks methods to api module

[federicobond]

This change does something similar to #164 but for the hooks API. Imports should be updated from:

from open_feature.hooks import api_hooks, add_api_hooks

To:

from open_feature.open_feature_api import get_hooks, add_hooks

This ensures all API-level methods are accessible from the same module.

[codecov]

Codecov Report

Merging #169 (49a9c79) into main (9e1bcb3) will decrease coverage by 0.68%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #169      +/-   ##
==========================================
- Coverage   94.15%   93.47%   -0.68%     
==========================================
  Files          24       23       -1     
  Lines         462      460       -2     
==========================================
- Hits          435      430       -5     
- Misses         27       30       +3     

Flag	Coverage Δ
unittests	93.47% <100.00%> (-0.68%)	⬇️

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Files Changed	Coverage Δ
open_feature/open_feature_client.py	95.87% <ø> (-0.05%)	⬇️
open_feature/open_feature_api.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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