Support converting `std::path::{Path, PathBuf}` to `pathlib.Path`

[Ravencentric]

For example, take this very simple rust function. Calling it from python will result in PathBuf getting converted to builtins.str instead of pathlib.Path. My feature request is that it should instead convert to pathlib.Path.

fn get_parent_directory(path: PathBuf) -> PyResult<PathBuf> {
    let dir = match path.as_ref().parent() {
        Some(parent) if parent == Path::new("") => Path::new("."),
        Some(parent) => parent,
        None => Path::new("."),
        };

    let dir = dunce::canonicalize(dir).map_err(|e| PyOSError::new_err(e.to_string()))?;
    Ok(dir)
}