impl(oauth2): omit RAB header when locations unbounded

[scotthart]

If the returned encoded_locations has a value of 0x0, then omit the x-allowed-locations header altogether.

[gemini-code-assist]

Code Review

This pull request introduces the IsUnbounded helper method to AllowedLocationsResponse to check if the encoded locations are set to '0x0'. It updates RegionalAccessBoundaryTokenManager to omit the x-allowed-locations header when the locations are unbounded, and adds a corresponding unit test to verify this behavior. I have no feedback to provide as the changes are well-implemented and include appropriate test coverage.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.70%. Comparing base (458cbf4) to head (2d2119f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16136      +/-   ##
==========================================
- Coverage   92.72%   92.70%   -0.02%     
==========================================
  Files        2356     2356              
  Lines      220497   220517      +20     
==========================================
- Hits       204448   204441       -7     
- Misses      16049    16076      +27     

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