pyproject packaging improvements
    
    - don't BR setuptools manually, this package uses poetry
    - don't use %pyproject_save_files '*' +auto, it is not encouraged in Fedora
    - put %generate_buildrequires after %prep, where it happens
    - remove the stay .orig file in %prep to avoid having it listed in %{pyproject_files}
    
    Signed-off-by: Ankur Sinha (Ankur Sinha Gmail) <sanjay.ankur@gmail.com>