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
- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.
If you need help, consider asking for advice on the #hackers-devrel
channel on [Discord].
<!-- Links -->
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Style-guide-for-Flutter-repo.md
[CLA]: https://cla.developers.google.com/
[Discord]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Chat.md
[Contributors Guide]:
https://github.com/flutter/samples/blob/main/CONTRIBUTING.md