fix(weave): Add support for class saving in ipython

[andrewtruong]

Resolves:

• https://wandb.atlassian.net/browse/WB-19574

This PR adds support for saving classes that are created inside an interactive environment.

Previously, we would raise an error like:

TypeError: Source for <class '__main__.MyClass'> not found

This seems to be a common issue raised in ipython:

• https://github.com/ipython/ipython/issues/11249
• https://bugs.python.org/issue33826
• https://stackoverflow.com/questions/51566497/getting-the-source-of-an-object-defined-in-a-jupyter-notebook/65806216#65806216

The solution suggested in the threads above will not work with classes that don't have methods. The approach here works for all classes, which is helpful because BaseModels can be used like plain structs (with no methods)

TODO: This PR needs a nb test

[circle-job-mirror[bot]]

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