Hi!

While rebuilding the python related packages against the Python 3.15rc2
version we found that datalad fails to build from source [1].

The error was:
Download error on https://pypi.org/simple/keyrings.alt/: [Errno -3] Temporary failure in name resolution -- Some packages may not be found!

To fix this and other issues, I had to make a number of changes to the
package:
- Make sure it doesn't use the network while building
- Add upstream patch 8f078923de85308307efbd5ea1f1cfa199d8d190: fix:
   Avoid use of return in a finally block
- Add patch to use fork with multiprocessing, avoid using the forkserver
- Avoid using the setuptools deprecated develop call
- Ignore commonprefix deprecation warning
- Update PYBUILD_BEFORE_TEST to ensure bin/ shims are regenerated

I've applied these fixes in the sandbox [2] to verify that it builds
successfully, please consider applying the patch to support the upcoming
3.15 version.

Setting the severity to important for now. Once Python 3.15 is released,
it will be added to python3-defaults and this bug will become release
critical.

Happy hacking,

[1]: https://debusine.debian.net/debian/r-python-python3.15/artifact/4514128/
[2]: https://debusine.debian.net/debian/r-python-python3.15/