rhino3dm: add build-rhino3dm.yml for riscv64 wheels

[luhenry]

• Package: rhino3dm
• Version: 8.32.1
• Source: https://github.com/mcneel/rhino3dm
• Docs: https://github.com/mcneel/rhino3dm

pybind11 wrapper around OpenNURBS (McNeel's 3D geometry library) and Draco mesh compression, both vendored as git submodules and statically linked. Upstream publishes no riscv64 wheel.

Mirrors the build_py_manylinux job of upstream's workflow_release.yml.

Differs from upstream

• Checked out at a commit, not a tag - 8.32.1 was never tagged in git; the commit's tree is byte-identical to the released sdist.
• cmake installed via CIBW_BEFORE_BUILD - setup.py shells out to it directly and it is not a declared build requirement anywhere upstream.

Testing

• same as upstream

License: Wheel bundles rhino3dm's own MIT LICENSE plus opennurbs, draco (Apache-2.0) and pybind11 (BSD) LICENSE files, staged at the checkout root for setuptools' default license_files glob.

Built on cp312; results pending CI.