[Compass App] Cleanup and extra tests

[miquelbeltran]

Some changes to make the project ready to merge to main

• Fix formatting.
• Add project to the stable channel CI (potentially could be added for beta and master)
  • CI only runs when targeting main, so I run the command locally and it worked.
• Add unit tests for the ApiClient and AuthApiClient which had no test coverage outside of integration tests.
• Resolved some TODOs I left before.

Pre-launch Checklist

• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I read the Contributors Guide.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.

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