ci: switch riscv64 from QEMU to native RISE runner

[gounthar]

Switch riscv64 wheel builds from QEMU emulation (~6h) to native RISE runners.

Changes:

• runs-on: ubuntu-latest + QEMU replaced with runs-on: ubuntu-24.04-riscv (native hardware)
• Removed docker/setup-qemu-action step
• Use pipx run cibuildwheel on riscv64 to bypass the GitHub Action's setup-python call (not yet available for riscv64)
• Other platforms unchanged

The RISE GitHub App is already installed on the rapidfuzz org.

Addresses the build time concern from #474.

[maxbachmann]

Thanks

[maxbachmann]

As an update it still takes a bit more than 3h for the build but presumably simply because the risc runners are less powerful. Since this only runs on release anyway the time itself isn't really a concern and I mostly didn't want to waste resources. Even more so because the hardware is sponsored by RISE which is the organization that wants this in the first place.