rapidyaml: add build-rapidyaml.yml for riscv64 wheels

[luhenry]

• Package: rapidyaml
• Version: 0.15.2
• Source: https://github.com/biojppm/rapidyaml-python
• Docs: https://github.com/biojppm/rapidyaml-python

Compiles a SWIG-generated CPython extension wrapping the vendored ryml C++ YAML library (git submodule) via CMake. Upstream publishes no riscv64 wheel.

Mirrors upstream's release.yml.

Differs from upstream

• Nothing beyond the riscv64 image and the shallow-checkout setuptools_scm pin.

Testing

• same as upstream

License: OK

Local pip wheel build (macOS) produced a real wheel with a compiled _ryml.so; installed it and ran pytest test (236 passed).