Support python 3.13

[ap--]

Support Python 3.13 on the v0.2.x branch of universal-pathlib.

Closes #221, closes #245

The final 3.13 release is pretty close, so it's better to add support for downstream packages to be able to test.

TODOs:

• should probably add the stdlib tests for 3.13 too to be consistent.
• update classifiers in pyproject.toml
• figure out why boto3 wont install on windows 3.13

MISSING SUPPORT UPSTREAM

• Windows tests can't run because the python docker package relies on pywin32 and there are no wheels for 3.13 yet

[ap--]

On Windows we need to wait for pywin32 xref: mhammond/pywin32#2367 mhammond/pywin32#2294

[ap--]

Windows tests on 3.13 succeed when installing pywin32 from here: https://github.com/mhammond/pywin32/actions/runs/9733348106/artifacts/1652979372

Once mhammond/pywin32#2294 is completed we can enable tests