Accept transformer methods with no __name__ in Pipelines

[HugoPerrier]

Description of Problem:

melusine/base.py:238: in transform
logger.debug(f"Running transform for {type(self).__name__} ({method.__name__})")

If the name attribute is absent, the transform method execution fails.
This may happens for mocked methods.

Overview of the Solution:
Use a default name if the name attribute is not present

Definition of Done:
Transformers with unnamed methods can be run.