python: publish linux-aarch64 wheels on native ARM runners

[thellert]

linux-aarch64 wheels for the EPICS PVA stack

There is no linux-aarch64 wheel on PyPI for epicscorelibs, pvxslibs or p4p, at any interpreter. All three publish macosx_11_0_universal2, manylinux2014_x86_64 / manylinux_2_28_x86_64 and win_amd64 only. So on arm64 Linux pip install p4p source-builds all three and needs a C toolchain on the host. A container image can stage one; a bare-metal install cannot be assumed to have one.

Three PRs, one per repo, adding the missing rows:

• Publish linux-aarch64 wheels on native ARM runners epicscorelibs#56 — epicscorelibs
• python: publish linux-aarch64 wheels on native ARM runners #201 — pvxslibs
• Publish linux-aarch64 wheels on native ARM runners p4p#226 — p4p

They need to merge in that order: pvxslibs builds against epicscorelibs, and p4p against both. Until the one above it has merged and published, each downstream PR's aarch64 jobs are expected to fail — see the note in each.

Why now. epics-base/epicscorelibs#21 and #48 proposed this in 2023 using QEMU, and were closed unmerged in favour of waiting for ARM-based hosted runners. Those runners are now generally available and free on public repositories, which removes both objections raised in that discussion: the build is native rather than ~40 minutes emulated, and the unit tests run against a real kernel, so qemu-user not translating IP_MULTICAST_ALL, SO_RXQ_OVFL, IP_MULTICAST_IF and IPV6_MULTICAST_IF is no longer a factor.

The change, identical in all three:

• runs-on: ${{ matrix.runner || 'ubuntu-latest' }}, following the existing ${{ matrix.cy || 'Cython' }} idiom, so the x86_64 and native rows are untouched.
• New manylinux2014_aarch64 rows for cp39–cp313 and manylinux_2_28_aarch64 for cp314/cp314t, mirroring the x86_64 set, each with runner: ubuntu-24.04-arm.
• Nothing cross-compiles: ubuntu-24.04-arm builds linux-aarch64 natively. (epics-base/ci-scripts already builds that target, as a cross-compile.)
• podman 5.8.4 is preinstalled on ubuntu-24.04-arm, the same version as on the x64 image, so the podman run step is unchanged.
• mdavidsaver/ci-core-dumper@master is a node24 action and GitHub-provided runtimes are arm64-native, so it needs no change.
• Artifact names already include matrix.ml, so nothing collides, and src: true stays on the x86_64 cp314 row only.

This repo

Second in the chain. Continues #48, which was closed unmerged in Oct 2023 in favour of native runners.

Expect the aarch64 rows to fail on this PR until epics-base/epicscorelibs#56 merges and publishes. The existing download line already carries --only-binary epicscorelibs, so with no aarch64 wheel available pip download fails immediately with a resolver error naming it, rather than falling back to the sdist. That is the intended behaviour and it costs almost no runner time. A re-run once epicscorelibs publishes should be clean; every other row is unaffected.