removed extract_source_code, it was only used in tests
add support to spy on Callable
supports to spy on Callable on all functions exclusive callv and call_deferredcall and call_deferred are not possible to stub because of interface conflicts between Callable and Object
Why
see https://github.com/MikeSchulze/gdUnit4/issues/544
What
extract_source_code, it was only used in testsCallablecallvandcall_deferredcallandcall_deferredare not possible to stub because of interface conflicts betweenCallableandObject