Objo projects can now be unit tested in Studio and CI

Add first-class, optional unit testing across Objo Engine, Objo Studio, and the objo command-line tool. Developers can create, discover, run, debug, filter, and understand synchronous, asynchronous, and headless desktop tests in Studio, then run the same isolated suites in CI with stable human, JSON, and JUnit output. Test sources and testing APIs remain excluded from normal application builds and published apps.