old_contents: from .builder import model_builder
  from .models import Model
  
  __all__ = ('Model', 'model_builder')
  
new_contents: from .builder import model_builder, model_many_builder
  from .models import Model
  
  __all__ = ('Model', 'model_builder', 'model_many_builder')
  
subject: Add missing function model_many_builder() to simple_model.__init__