Updated the pyo3 module in chronik-plugin-impl/tests/Cargo.toml.
The old syntax PyModule::from_code_bound() takes in a &str. With the new change to PyModule::from_code(), we need to take in a &CStr.
Therefore, created a function that converts from &str -> &CStr.
The other changes to call, new, import and empty are only renamed to keep the syntax up to date.