Minor fixes

[ewanharris]

Description

This PR fixes some minor issues I noticed while updating the openfga/api sha on `main. Splitting out to a separate PR to help review.

They are as follows:

• the ListUsers API differs on the shape of contextual_tuples, rather than an object with a tuple_keys property it just takes the array directly. So we don't need the ContextualTupleKeys type
• read_latest_authorization_model errors if there are no models
• list_users in the example was using the wrong types

References

openfga/sdk-generator#446

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

If you haven't done so yet, we would appreciate it if you could star the OpenFGA repository. :)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.15%. Comparing base (e49a77a) to head (8905252).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #147      +/-   ##
==========================================
- Coverage   69.17%   69.15%   -0.02%     
==========================================
  Files         122      122              
  Lines        9751     9753       +2     
==========================================
  Hits         6745     6745              
- Misses       3006     3008       +2     

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