Add Python 3.12 support; drop Python 3.7 support

[tseaver]

No description provided.

[dataflake]

Is there a specific reason you are removing Python 3.7 support? I don't see a technical reason, the tests run fine on Python 3.7.

Generally, we are using the config-package.py script from https://github.com/zopefoundation/meta/tree/master/config to make packaging related changes for any zopefoundation package, and we have not made the decision to remove Python 3.7 yet. We are moving closer, though.

Not using config-package.py and making changes manually turns a package into a one-off that requires extra work to maintain, so it's highly discouraged.

[tseaver]

As with the zdaemon PR, I'd be fine with re-adding 3.7 support if you prefer the consistency, but I'd like to hurry along the 3.12 support.

[dataflake]

Version 4.1 is now published.