cli/worker/tests: facade-only linkage and updated test suites

oak-cli and oak-render-worker use the C ABI exclusively (0 olive::
symbols). Google Test suites updated for the migrated APIs, new engine
facade test coverage, CLI transcode verification.

tests/gtest/viewer_display_repro_test.cpp

@@ -152,7 +152,7 @@ protected:
 		}
 
 		if (!Core::instance()) {
-			new Core(Core::CoreParams());
+			new Core();
 		}
 		AudioManager::create_instance();
 	}