Adding set_mode_info

[chapman20j]

What does this PR do?

Implements set_mode_info which displays information about the set_mode methods in a module.
This function recursively checks if nnx.Modules contain a set_mode attribute and collects the classes.
It then produces a string that contains information from the set_mode method signatures and docstrings from each module containing a set_mode method.

Fixes # (issue)

Checklist

• This PR fixes a minor issue (e.g.: typo or small bug) or improves the docs (you can dismiss the other checks if that's the case).
• This change is discussed in a Github issue/discussion (please add a link).
• [x ] The documentation and docstrings adhere to the documentation guidelines.
• [x ] This change includes necessary high-coverage tests. (No quality testing = no merge!)