Add support for Python 3.12

[hugovk]

The second and final Python 3.12 release candidate is out! 🚀

Call to action

We strongly encourage maintainers of third-party Python projects to prepare their projects for 3.12 compatibilities during this phase, and where necessary publish Python 3.12 wheels on PyPI to be ready for the final release of 3.12.0.

The final release is due in three weeks on 2023-10-02.

---

Bug report

Consider this a PR a bug report, the Python 3.12 build fails:

=================================== FAILURES ===================================
__________________________________ test_curio __________________________________

    @pytest.mark.skipif(
        os.name == "nt" and sys.version_info >= (3, 9),
        reason="Curio breaks on Python 3.9+ on Windows. Fix was not released yet",
    )
    def test_curio():
>       import curio

../../../../venv-3.12/lib/python3.12/site-packages/sniffio/_tests/test_sniffio.py:67: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../../../venv-3.12/lib/python3.12/site-packages/curio/__init__.py:6: in <module>
    from .queue import *
../../../../venv-3.12/lib/python3.12/site-packages/curio/queue.py:20: in <module>
    from . import workers
../../../../venv-3.12/lib/python3.12/site-packages/curio/workers.py:23: in <module>
    from .channel import Connection
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

    # channel.py
    #
    # Support for a message passing channel that can send bytes or pickled
    # Python objects on a stream.  Compatible with the Connection class in the
    # multiprocessing module, but rewritten for a purely asynchronous runtime.
    
    __all__ = ['Channel']
    
    # -- Standard Library
    
    import os
    import pickle
    import struct
    import hmac
    import multiprocessing.connection as mpc
    import logging
    
    log = logging.getLogger(__name__)
    
    # -- Curio
    
    from . import socket
    from .errors import CurioError, TaskTimeout
    from .io import StreamBase, FileStream
    from . import thread
    from .time import timeout_after, sleep
    
    # Authentication parameters (copied from multiprocessing)
    
    AUTH_MESSAGE_LENGTH = mpc.MESSAGE_LENGTH    # 20
>   CHALLENGE = mpc.CHALLENGE                   # b'#CHALLENGE#'
E   AttributeError: module 'multiprocessing.connection' has no attribute 'CHALLENGE'. Did you mean: '_CHALLENGE'?

This is because dependency curio doesn't support Python 3.12 yet. This issue/PR has suggestions how to fix it: dabeaz/curio#361 / dabeaz/curio#363.

Further:

Important Notice: October 25, 2022

The Curio project is no longer making package releases. I'm more than happy to accept bug reports and may continue to work on it from time to time as the mood strikes. If you want the absolute latest version, you should vendor the source code from here. Curio has no dependencies other than the Python standard library. --Dave

So you'll need to either vendor and fix curio, or replace it with something else.

Feel free to use this PR as a starting point for fixing it as you see best, or close this as needed.

Thanks!

[codecov]

Codecov Report

Merging #42 (d0c6b59) into master (0cfdab8) will not change coverage.
The diff coverage is n/a.

❗ Current head d0c6b59 differs from pull request most recent head d44c25b. Consider uploading reports for the commit d44c25b to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #42   +/-   ##
=======================================
  Coverage   96.51%   96.51%           
=======================================
  Files           4        4           
  Lines          86       86           
  Branches       17       15    -2     
=======================================
  Hits           83       83           
  Misses          2        2           
  Partials        1        1           

[njsmith]

can you mark the test skipif(sys.version >= (3, 12), reason="curio broken on 3.12 (https://github.com/python-trio/sniffio/pull/42)"? then we could merge as-is

[hugovk]

Now skipped. We could also skip installing the package for 3.12+?

Also removed the older Windows/3.9+ skip because the fix it was waiting for was released in the final curio on PyPI.

I also forgot to add 3.12 to the CI for macOS, so have added that too.

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