test: integrate tests directly into bindings

[ianprime0509]

This removes the separate test package in favor of including a test step in the generated bindings themselves. Besides simplicity, a major advantage of this approach is that doctests can be written for extensions and show up in the generated documentation.

TODO:

• Ensure members of types (methods, etc.) are also referenced during the test step
• Make it so that all the tests will actually pass (either by skipping broken modules or by fixing the underlying issues)
• Figure out what to do with the ABI tests
• Actually remove the test package

[ianprime0509]

Integrated in other commits pushed to main.