test: Improve test coverage for pagination async iteration

[allenporter]

Adds unit tests covering async iteration over multi-page paginated results in pagination.py.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.58%. Comparing base (e60d657) to head (2e48e0e).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
+ Coverage   82.09%   82.58%   +0.48%     
==========================================
  Files          30       30              
  Lines        3100     3100              
==========================================
+ Hits         2545     2560      +15     
+ Misses        555      540      -15     

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