ci: add riscv64 manylinux wheel builds

[gounthar]

Add native riscv64 wheel builds using RISE RISC-V runners (ubuntu-24.04-riscv) — no QEMU emulation.

Changes

• New manylinux-riscv64 job in wheel-builder.yml
• Uses native RISE riscv64 runners (as discussed — no QEMU)
• Installs Rust via rustup, Python from /opt/python-3.12
• Cargo registry cached across runs
• Same smoke test as existing jobs

Evidence

• Build time: ~5.5 minutes on native hardware
• Validated on RISE fork: ci: add native riscv64 wheel builds using RISE runners riseproject-dev/bcrypt#1
• Native build on BananaPi F3 (SpacemiT K1, rv64gc): SUCCESS
• RISE runners provided by Ludovic Henry / RISE project (free for open source)

Context

Updated per @reaperhulk's feedback — switched from QEMU to native runners.

Related: riscv64 Docker images for pyca infra: pyca/infra#748

[reaperhulk]

Thanks for the contribution but we won’t ship wheels for architectures we don’t test. For CI we require native (and ephemeral) runners with sufficient performance as a general rule to keep our CI pleasant to use, so qemu isn’t an option there unfortunately.

[gounthar]

@reaperhulk Understood, makes total sense. Native riscv64 runners are becoming available through RISE, which provides free ephemeral self-hosted runners on real hardware. I'll revisit this once those are ready for pyca. Thanks for considering it.

[gounthar]

@reaperhulk Updated. Switched from QEMU to native riscv64 runners provided by RISE. Build time is ~5.5 minutes on real hardware. Validated on a fork: riseproject-dev#1

Also opened pyca/infra#748 for the riscv64 Docker images needed for the full pyca build pipeline.

[gounthar]

@luhenry Thank you for enabling the RISE riscv64 runners that made this possible. Would it be possible to add native runners for the pyca organization as well? That would unblock riscv64 wheels for cryptography, bcrypt, and pynacl, three of the most downloaded packages on PyPI.

[luhenry]

@luhenry Thank you for enabling the RISE riscv64 runners that made this possible. Would it be possible to add native runners for the pyca organization as well? That would unblock riscv64 wheels for cryptography, bcrypt, and pynacl, three of the most downloaded packages on PyPI.

I’ll add them tomorrow. Now that we have access to more runners I’ll make sure to lift the restriction on registered organizations