`bind` directive skips metaclass logic

[jjotero]

#2083 introduced some changes in the metaclass that lead to functions imported with the bind directive to skip all the logic in the metaclass namespace assignment method. This means that, for example, adding a pipeline hook as follows would not work:

class MyTest(...):
   ...
   run_before(<a_pipeline_stage>)(bind(<an_external_free_function>))

This is because the external function is bound with the bind directive and the run_before is executed after that, which means that this method wouldn't be picked up as a pipeline hook.