Fix!: include names of decorator argument references when building python env

[georgesittas]

Fixes #3640

The main difficulty in solving the linked issue was making SQLMesh detect the stop_after_attempt reference, in order to extract and inject it into the python environment so it can be (de)serialized:

@retry(stop=stop_after_attempt(3))
def fetch_data():
    return "test data"

The decorator names themselves were already being picked up in the previous decorators helper. In this PR I expand that functionality by also searching for the decorator call arguments' references.

I implemented a new visitor class in order to limit the search to only the decorator sub-trees, instead of traversing the whole function tree. Without this, we'd have to do a nested walk within the root node traversal loop, leading to unnecessarily revisiting nodes under the decorator sub-trees.

Other than that, I also made sure to exclude callable instances of classes, because they can't be serialized. One such example is the tenacity.Retrying class (source). Letting these instances into the python environment doesn't "just work" unfortunately, because an error is raised once we reach this section, since there's no __name__ attribute in them.

I verified that this fix works for a project with the model of interest, as well as the example project we have under test_metaprogramming.py.