CI smoketest on a virtualized A55 CPU

[mcm001]

In https://github.com/PhotonVision/mrcal-java/pull/27/changes we added some flags to make sure our Arm64 builds targeted armv8-a, because the Github Actions runner we build on's native architecture includes instructions illegal to run on Orange Pi 5/Pi devices. Let's add a CI test to make sure that we can run on a simulated cortex A55 CPU.

This adds 27 seconds of runtime -- 21 to run the test under QEMU, and 6 to install packages. Windows is still critical path at 10.5 minutes, though

[Copilot]

Pull request overview

This PR updates CI to execute an ARM64 smoketest of mrcal_jni_test under qemu-aarch64 (Cortex-A55), and reduces the runtime of the native test executable to better fit CI constraints.

Changes:

• Reduce the mrcal_jni_test loop iteration count (5 → 1) to shorten execution time.
• Extend the build workflow to run mrcal_jni_test and to stage/upload ARM64 binaries and shared-library artifacts.
• Add a follow-on job that downloads the ARM64 artifacts and runs the test under QEMU with -cpu cortex-a55.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/mrcal_test.cpp	Reduces test/benchmark iteration count to speed up CI smoketests.
.github/workflows/main.yml	Builds/runs native test, stages ARM64 runtime artifacts, and adds a QEMU A55 execution job.

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