Add informal Python 3.13 support

[jrmccluskey]

Introduces the changes to the package itself, gradle, and tox definitions to include Python 3.13 support. Does not automatically create or publish python 3.13 containers, nor does it add Python 3.13 testing to GitHub Actions workflows (hence the term "informal support.") Actions workflow updates will be done in a follow-up with changes living on a branch of the mainline Beam repo for testing on our runners.

Part of #34869

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[tvalentyn]

was this line manually edited to install an RC version? does it have the fix?

[jrmccluskey]

that was not intended, I generated this file with the generatePythonRequirements workflow and it seems to pick up RC versions when I don't want it to. I bumped it back down to 1.71.0

[tvalentyn]

could you remind me please, what is the impact of this change?

[jrmccluskey]

This is one I genuinely just saw while I was going through the code base and updated (since 3.8 hasn't been the max supported python version in quite some time.) I don't think the variable is particularly load bearing since we haven't been using 3.8 for months