unitbase.gd now sets 'config.logger_level = CoreTypes.LoggerLevel.DIAG' and checks in 'unload_framework()' if the test was skipped and if so it does not crash.
Good that I decided to introduce unit tests to CORE because I found multiple issues in the Scene Manager which I was now able to fix. See 52c6d029d9, 25c4667a05 and 32b82c8f5b.
A better version of the 'z_cleanup' test has been integrated into Bessere Tests in the latest commit (as of writing this commit message). Therefore this test is no longer required as Bessere Tests will warn us on shutdown for any leftover children or orphan nodes from now on.
