Update objcryst version for 2026.1, exposing SetPowderPatternObsSigma

[vincefn]

Note: unless I'm wrong, libobjcryst does not use the same commit hooks which use news/... files automatically ?

This is needed for a new release and diffpy/pyobjcryst#84.

[sbillinge]

@vincefn that's right. It looks as if we started that conversation here. I checked, we also don't give libdiffpy this treatment either. As a general matter I would be interested in moving those projects over in this direction so we have fewer "outliers" that need special treatment, but for sure now is not the right time.

Do you think it would be a good idea, in principle, to do this migration? We could do it onto a migration branch and not into main, so we could abort at any time. We could also try and do libdiffpy first to see what we run into. Of course we could also look into giving the love to any sub-packages.

We may want to work on what we consider linting standards for c++ too before we get too far with this.

In other respects this PR looks good to me. Please go ahead and merge it (or I can if you prefer) and go ahead with that release.

[vincefn]

It could be interesting to include a pre-commit, but it would have limited effects as it would not affect the upstream ObjCryst - so the lightweight pre-commit from #21 would need to exclude all the upstream code, and a similar pre-commit could be added to the ObjCryst project.