fix: set the consistency parameter correctly in OpenFGAClient

[ewanharris]

Description

In #129 I somehow overlooked setting the consistency parameter on the underlying API request body, this correctly does that and then adds tests to ensure that this is carried through as expected.

References

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

All modified and coverable lines are covered by tests ✅

Project coverage is 88.13%. Comparing base (15829c3) to head (1370a12).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #143   +/-   ##
=======================================
  Coverage   88.13%   88.13%           
=======================================
  Files          19       19           
  Lines        1003     1003           
  Branches      150      133   -17     
=======================================
  Hits          884      884           
  Misses         82       82           
  Partials       37       37           

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