[freakboy3742]

Add CI for Python 3.16.

Compatibility changes:

• A bump to the PySide6 bootstrap template; PySide6 6.12.0 includes Python 3.15 support, but requires a minimum macOS version of 14.0.
• urlparse() now raises a warning if passed a non-string value. Anything that isn't a string can be rejected as "not a URL".
• shutil.unpack() can now accept wheels; anywhere that we're asking if a file is an archive, if it's a wheel we need to install as a wheel, not unpack.

Also downgrades support for macOS on Intel to "best effort" support, removing CI configurations.

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

[mhsmith]

This behavior contradicts the docstring of is_archive. I see it was changed to pass the existing tests, but would it make more sense to update the tests? Looking at the places where this function is used, it doesn't look like they need to distinguish between .whl files and other archives.

[freakboy3742]

Looks like I misread the logic around usage here; I thought we needed to exclude wheels to trigger the right logic in the venv backends, but on re-reading, I can see that isn't the case. I've reverted this and modified the expected test result to be version sensitive.

[freakboy3742]

Since there were other updates needed to this PR, I've taken the opportunity to drop macOS Intel testing as well.

It turns out the templates have already dropped Intel runners.