ci: implement native multi-arch builds and smoke tests (x86_64 & arm64)

[rkt0209]

Overview

This PR implements a native, multi-architecture GitHub Actions CI pipeline for the CUPS snap, specifically targeting x86_64 and arm64.

Technical Implementation

• Native Build Matrix: * Implemented a strategy.matrix to execute builds natively without emulation.

  • x86_64 utilizes standard ubuntu-latest runners.
  • arm64 utilizes GitHub's native ARM runners (ubuntu-24.04-arm).

• Automated Smoke Testing: * Added post-build runtime validation directly on the runner host:

  • Mounts and installs the compiled snap: sudo snap install --dangerous <dynamic-snap-path>.
  • Verifies system registration: snap list | grep "^cups ".
  • Validates binary execution and internal paths: snap run cups.gs -h.

• State Teardown: * Implemented a guaranteed cleanup step (if: always()) executing sudo snap remove cups to maintain pristine runner environments post-test, regardless of test outcome.