jsonschema-rs: add build-jsonschema-rs.yml for riscv64 wheels

[luhenry]

• Package: jsonschema-rs
• Version: 0.52.0
• Source: https://github.com/Stranger6667/jsonschema
• Docs: https://github.com/Stranger6667/jsonschema/tree/master/crates/jsonschema-py

Compiles jsonschema-py, the PyO3 bindings crate in the jsonschema monorepo — a Rust-backed JSON Schema validator for Python. Upstream publishes no riscv64 wheel.

Mirrors the linux job of upstream's python-release.yml.

Differs from upstream

• musllinux dropped - rustup ships no riscv64 musl toolchain.
• Rust toolchain installed in-container rather than on the runner.
• LICENSE staged beside crates/jsonschema-py/pyproject.toml so it reaches the wheel.

Matrix: cp310-abi3 (pyo3 abi3-py310 is unconditional, built on cp310 and re-tested on cp311-cp314) plus cp314t; cp313t is absent from the riscv64 image.

Testing

• test_http_fetch_external_schema deselected - needs a live json-schema.org endpoint.
• JSON-Schema-Test-Suite submodule and the module's README staged alongside tests-py so the suite runs unmodified.

License: MIT; upstream ships no licence text in the wheel (maturin's glob is relative to the pyproject directory), so the build adds it.

Built on cp310-abi3 and cp314t; ~9445 passed, 1 deselected, 1 xfailed.