fiona: add build-fiona.yml for riscv64 wheels

[luhenry]

• Package: fiona
• Version: 1.10.1
• Source: https://github.com/Toblerity/Fiona
• Docs: https://fiona.readthedocs.io/

Cython bindings over GDAL for vector I/O. Upstream publishes no riscv64 wheel.

Fiona ships no in-repo wheel workflow; mirrors sgillies/fiona-wheels' build shape and the docker_tests job of upstream's tests.yml.

Differs from upstream

• GDAL/GEOS/PROJ/SpatiaLite built once into a shared image, not per vcpkg/multibuild job - no riscv64 binary cache.
• Same image shape as build-pyogrio.yml (BUILD_APPS=OFF) - fiona's setup.py only needs gdal-config, which GDAL's CMake build generates either way.

Matrix: cp312/cp313 - fiona's own PyPI wheels for 1.10.1 stop at cp313, matching its cython~=3.0.2 pin's last release.

Testing

• wheel-marked tests included, not skipped - upstream only skips them for its own source installs.

License: wheel bundles GDAL, GEOS, PROJ and SpatiaLite plus the rest of the image's shared-library closure, all permissively licensed.

Built on cp312; CI results pending.