protovalidate: add build-protovalidate.yml for riscv64 wheels

[luhenry]

• Package: protovalidate
• Version: 2.0.0
• Source: https://github.com/bufbuild/protovalidate-py
• Docs: https://protovalidate.com

Compiles a PyO3 extension that statically links six vendored C++ projects (abseil-cpp, antlr4, cel-cpp, protobuf, re2, protovalidate-cc) into a CEL-based protobuf validator. Upstream publishes no riscv64 wheel.

Mirrors upstream's release.yaml, using cibuildwheel instead of maturin-action directly.

Differs from upstream

• musllinux dropped - rustup ships no riscv64 musl toolchain.

Testing

• test pyproject.toml staged to keep the root protovalidate/ source tree from shadowing the installed wheel's compiled extension
• pytest/pytest-benchmark/pydantic pinned to upstream's dev-required versions; protobuf (Google's package, legacy conformance coverage) pulled from our registry

License: wheel statically links abseil-cpp/cel-cpp/protovalidate-cc (Apache-2.0) and antlr4/protobuf/re2/utf8_range (BSD-3-Clause/MIT); upstream's license-files names only its own LICENSE, so a patch adds the six vendored ones.

Patches

• 0001-list-vendored-c-licence-files-in-project-license-fi.patch - To upstream, not submitted (session policy). Without it every published wheel ships none of the six vendored licence texts. Reproduces on any platform, not riscv64-only.

CI running; test counts to follow once green.