- Introduce a GitHub Actions matrix for `test-container` and `test-e2e`
to run against arch, debian, ubuntu, fedora, and centos
- Run unit and integration tests only in the Arch container by passing
`distro="arch"` via make in the corresponding workflows
- Replace the global DISTROS loop with a single `distro` variable in
the Makefile, defaulting to `arch`, and export it for all scripts
- Update build scripts (build-image, build-image-no-cache, build-image-missing)
to build images for the selected distro only
- Simplify test-container script to validate a single distro image using
the `distro` environment variable
- Simplify E2E, unit, and integration test scripts to run against a
single distro container instead of iterating over all distros
https://chatgpt.com/share/693acbba-9e30-800f-94fb-fea4489e9078
