Add linux_aarch64 platform

[christianbundy]

Problem

We aren't building wheels for linux_aarch64, which is a commonly used architecture. For example, when using Docker on an Apple M1 Pro:

$ docker run ubuntu uname -sm
Linux aarch64

Solution

Add aarch64 to CIBW_ARCHS_LINUX, add QEMU for emulation, and add an override to cibuildwheel.toml that runs only testcheck. This takes about 90 minutes for manylinux and 2 hours for musllinux.

---

See-also: #37

[achimnol]

@christianbundy @hauntsaninja Now we have native arm64 GitHub Actions runners for Ubuntu and Windows.
https://github.blog/2024-06-03-arm64-on-github-actions-powering-faster-more-efficient-build-systems/
This requires the large github runners setup in the repository or organization. Once done, this PR could avoid using the qemu action but use the native arm64 runner.

[komapa]

Hello, is this closer to being merged? Thank you!