Update to declarative python modules

[tdittr]

This makes it look even simpler. See PyO3 docs

rust-training/slides/7_1-rust-from-python.md

Lines 197 to 201 in 46f62a3

	#[pymodule]
	fn hello_py(_py: Python<'_>, m: &Bound<'_, PyModule>) -> PyResult<()> {
	m.add_function(wrap_pyfunction!(say_hello, m)?)?;
	Ok(())
	}