Python version update for Transcrypt: 3.13

[JennaSys]

WIth Python version 3.9 reaching end-of-life this year, Transcrypt is currently being updated to be compatible with Python 3.13

All automated and manual tests are currently passing.

If you wish to try it out before it is released, you can install it from the development branch with:
pip install git+https://github.com/TranscryptOrg/Transcrypt@dev_3.13.0

There are no feature adds with this release beyond the 3.9.4 version other than ensuring compatibility with the Python 3.13 AST module.