Updates for Python 3.x, Flask 3.x

[jhamlin96]

I recently used this library and wanted to use the latest version of Python and Flask, so I performed the syntax updates for Python 3.x and Flask 3.x. Tested on 3.11 / Flask 3.1.0. Updated the unit tests and ensured all passed. Thanks!

[mc51]

Thanks a lot @jhamlin96, this has really helped me!
I'm probably one of the few people that still depend on this. It was a real pain to still make this work with any python version >3.9. And even there, dependencies and errors would really bug me. Now, I managed to make this work with python 3.12, migrate to uv, and deploy as a docker container in lambda.