ast-grep-py: add build-ast-grep-py.yml for riscv64 wheels

[luhenry]

• Package: ast-grep-py
• Version: 0.45.2
• Source: https://github.com/ast-grep/ast-grep
• Docs: https://ast-grep.github.io/

Compiles the ast-grep-py PyO3 extension (crates/pyo3 in the ast-grep monorepo) that binds ast-grep's core matching engine and its bundled tree-sitter grammars into a per-interpreter Python module. Upstream publishes no riscv64 wheel.

Mirrors upstream's pyo3.yml.

Differs from upstream

• Stages the repo-root LICENSE beside crates/pyo3/pyproject.toml before building - maturin globs licence files relative to the pyproject directory, so upstream's own published wheel carries none.
• musllinux dropped - rustup.rs ships no riscv64 musl host toolchain.

Testing

• same as upstream

License: OK

Built on cp312; 59 passed.