fastnanoid: add build-fastnanoid.yml for riscv64 wheels

[luhenry]

• Package: fastnanoid
• Version: 0.4.3
• Source: https://github.com/oliverlambson/fastnanoid
• Docs: https://github.com/oliverlambson/fastnanoid

Compiles the pyo3 Nano ID generator extension. Upstream publishes no riscv64 wheel.

Mirrors the linux job of upstream's CI.yml.

Differs from upstream

• Only manylinux, no musllinux - rustup.rs ships no riscv64 musl toolchain
• Rust toolchain installed in-container via rustup - upstream's maturin-action does this itself

Testing

• Runs upstream's tests/test_fastnanoid.py against the built wheel plus a compiled-extension check; upstream's own CI never installs or tests the wheel, only cargo test

License: OK