build/pkgs/boost_cropped: Switch upstream to scipy, update to 1.75.0

[mkoeppe]

📚 Description

https://github.com/scipy/boost-headers-only

Resolves #34748

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit 4f6f467; changes) is ready! 🎉

[dcoudert]

This looks good to me. Should we try to do more tests (and how) ?

[dimpase]

boost 1.75 is 2.5 years old. The current boost version is 1.82.0.

Why is scipy stuck in 1.75?

[dimpase]

anyhow, I reckon that all the platforms we support do ship a new enough boost, so this is a low-priority update of a vendored package.

I'd rather be getting rid of internal boost-cropped. There is always a chance that some Sage package will need more than this from boost, e.g. there are GAP packages which use boost...

[dcoudert]

At least this PR should simplify the management of this package.

[dimpase]

I think scipy has more or less abandoned their boost-headers only clone, and instead went with directly vendoring Boost.Math (the only thing they need), cf scipy/scipy#17432

[dcoudert]

oups. So then it's not a good idea to switch to this tarball :(