fix: inconsistence in 429 handling between sync/async client

[evansims]

Description

This change addresses inconsistencies between the sync and async clients when encountering HTTP status codes 429 or 400 in an HTTP response.

References

Closes #129

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 69.13%. Comparing base (e2ce832) to head (4915b57).

Files with missing lines	Patch %	Lines
openfga_sdk/rest.py	0.00%	2 Missing ⚠️
openfga_sdk/sync/rest.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #131      +/-   ##
==========================================
- Coverage   69.16%   69.13%   -0.03%     
==========================================
  Files         121      121              
  Lines        9982     9986       +4     
==========================================
  Hits         6904     6904              
- Misses       3078     3082       +4     

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[ewanharris]

Looks good!

I don't think we should handle in this PR as it might prove a larger task, but I wonder if we could move down a level in our mocking for tests as it seems we're mocking this request function currently which means we miss code like this.