Multi-stage Dockerfile.graalpy on ghcr.io/graalvm/graalpy-community:25
that builds the granian and rloop PyO3 extensions from source against
GraalPy (no GraalPy wheels exist), installs the pure-Python deps, and
serves the unchanged RSGI app on the rloop event loop.
Adds docker-compose.graalpy.yml and a CI job publishing the image as
the *-graalpy tags on release/*.
