ci: add riscv64 manylinux wheels with native RISE runners

[gounthar]

Summary

Add riscv64 manylinux wheel builds using native RISE RISC-V runners instead of QEMU emulation.

Based on the excellent work by @justeph in #227. This PR builds on that approach with native runner support for significantly faster builds.

Changes

• Add riscv64 matrix entries (cp39-cp314t) following the s390x pattern
• Use ubuntu-24.04-riscv native runner (no QEMU needed)
• Skip docker/setup-qemu-action for riscv64
• Add CIBW_MANYLINUX_RISCV64_IMAGE defaulting to manylinux_2_39 (first manylinux with riscv64)

Why native runners over QEMU

QEMU emulation (as in #227) works but is slow. Native RISE runners provide real riscv64 hardware at no cost to the project, with build times comparable to other architectures.

Evidence

• cffi 2.0.0 built successfully on native riscv64: BananaPi F3, SpacemiT K1, rv64gc, GCC 14.2.0
• RISE runners validated on numpy (3.5 min build), bcrypt, xet-core, and other projects

Credits

• @justeph for the initial riscv64 matrix entries in ci: add riscv64 manylinux wheels #227
• Ludovic Henry and the RISE project for native riscv64 runners

Supersedes #227

[gounthar]

Correction: the linked CI run was from the fork's own scheduled build, not RISE runners. However, the build succeeds on native riscv64. build time: ~2m39s (https://github.com/gounthar/cffi/actions/runs/23103252300). Also verified on BananaPi F3 hardware. The PR's native runner approach (ubuntu-24.04-riscv) is ready for when RISE runners are installed on the cffi org.

[gounthar]

Successful riscv64 build on native RISE runners (ubuntu-24.04-riscv): https://github.com/gounthar/cffi/actions/runs/23706627020

Build, wheel verification, and release all passed. Build time under 3 minutes on native hardware.

[justeph]

I guess we can remove ${{ env.skip_slow_jobs }} now it runs on native runners

[gounthar]

Good catch. Removed skip_slow_jobs from all riscv64 entries. Kept skip_ci_redundant_jobs for the intermediate Python versions, matching the pattern of the other architectures.

[justeph]

Also other non emulated targets don't specify test_args: '{package}/src/c' which seems to run only a subset of the test suite. Maybe we should remove it here also?

I started an action on my fork, and with the full test suite, riscv64 build takes 34 minutes (see https://github.com/justeph/cffi/actions/runs/23733528422/job/69141241075) compared to x86 which succeeded in 4 minutes..

For what it worth, this is still better than the 1 hour with emulation :) https://github.com/justeph/cffi/actions/runs/21716002341/job/62632136017

So makes me wondering if we should remove the skip_slow_jobs or running the full test suite?

But then, do we need native runners? Emulated riscv64 job with test_args: '{package}/src/c' runs in 5 minutes https://github.com/justeph/cffi/actions/runs/21716002341/job/62632136043 when it runs in 6 minutes on native runner https://github.com/justeph/cffi/actions/runs/23731763287/job/69126983344...

Maybe that will be a decision for @DimitriPapadopoulos or @mattip (or someone else 😅 ) ?

[gounthar]

Makes sense. Removed test_args so riscv64 runs the full test suite like the other native targets. 34 minutes is reasonable for a native build, and much better than the hour under emulation.