Rust File IO and RAII
Example code and expected result:

https://paste.ubuntu.com/p/dHFvZKdZmf/

Getting this to work requires us to:

* Implement some traits such as FileReadString for easier transpilation. These could go into a rust-pylib similar to nim-pylib in https://github.com/adsharma/py2many/issues/229
* Handle all the mapping cases including tempfiles
* import tempfile doesn't transpile well to the right extern crate and use statements
