infra: Move unit tests to a subdirectory to allow space for integration tests (#544)
* Move existing backend unit tests to new tests/unit directory
* Fix broken imports
* Only run the unit tests on pushes to main
* Specify that we're running unit tests
* Fix lint issues and try running unit tests without a deployment
* Move tests requiring a deployment out of the unit test directory
* Move over a few more tests from /unit to /integration
* Move more tests from /unit to /integration
* Fix import error
* Clean up unused imports
* Address some PR comments
* Add unit tests for request_validators, JWTs, and basic auth
* Remove automatic runner for integration tests
* Fix import
* Fix formatting
* Move more tests to /integration
* Move last 3 failing tests from /unit to /integration
* Fix styling
* Fix styling in Coral