Add better arch support + support ARM runners

[bleggett]

• Adds flavor-level arch overrides, so specific flavors can build with unique arch combos (e.g. zone-nvidiagpu = x86_64 only, zone= x86_64 + aarch64, etc)
• Prefer GH-supplied ARM runners for ARM kernel builds, instead of QEMU+edera-large crosscomp (experiment to see if this is actually faster - EDIT: as seen in CI it's equivalent to a coldcache build on edera-large, good enough)
• Add arch to the matrix buildscript args: ./hack/build/docker-build.sh "only-latest-lts:flavor=zone;arch=aarch64"
• by default, build only zone (standard) kernel for both x86_64 and aarch64, so we don't have to choose between cross-building everything or nothing, and can be selective about it.

[sveith]

Thank you for taking care of implementing the aarch64 builds.

I have some minor suggestions around the way shell escaping is done in this area of the code.

[bleggett]

Thank you for taking care of implementing the aarch64 builds.

I have some minor suggestions around the way shell escaping is done in this area of the code.

TY for reviewing - I'm absolutely not a python coder and do not wish to be one - do you have a recommendation for a good automated python linter/stylechecker we could add here that would autoflag most of this?

Many of these scripts are in various stages of mess and we probably need that regardless.

[sveith]

TY for reviewing - I'm absolutely not a python coder and do not wish to be one - do you have a recommendation for a good automated python linter/stylechecker we could add here that would autoflag most of this?

I think we're in a peculiar position here because we generate shell source code dynamically from within Python, and this crossover between languages makes it hard to lint for such issues in either language (we're not running Shellcheck on the outputs either).

I like Python, and I'll happily follow up with a cleanup of the shell escape issues that I've flagged above. Let's unblock your PR.

[bleggett]

I like Python, and I'll happily follow up with a cleanup of the shell escape issues that I've flagged above. Let's unblock your PR.

Thank you, and please feel free to add python stylechecking with automated CI utils according to your taste/best practice standards. In matters of taste, the configured CI linter always wins, and I am more than happy to let it.

[bleggett]

For ref, clean build outside of PR CI: https://github.com/edera-dev/linux-kernel-oci/actions/runs/25689245098