api/schema: get schema without having a machine

Also done:
- add @pytest.mark.with_core indicating that a test depends on clan-core and cannot be cached
- separate unit tests into two derivations, ones that can be cached and ones that cannot.
- fix frontend typescript code

pkgs/clan-cli/tests/test_clan_modules.py

@@ -3,7 +3,7 @@ from api import TestClient
 from fixtures_flakes import FlakeForTest
 
 
-@pytest.mark.impure()
+@pytest.mark.with_core
 def test_configure_machine(api: TestClient, test_flake_with_core: FlakeForTest) -> None:
     # retrieve the list of available clanModules
     response = api.get(f"/api/{test_flake_with_core.name}/clan_modules")