ci: add Linux and Windows aarch64 testing

Add ARM64 runners to the test matrix:
- ubuntu-24.04-arm for Linux aarch64
- windows-11-arm for Windows aarch64

This ensures the library builds and passes tests on ARM64, which is
increasingly important for:
- AWS Graviton instances
- Azure Cobalt / Arm-based VMs
- Docker on Apple Silicon
- Windows on ARM devices (Surface Pro X, etc.)
- Raspberry Pi and other ARM SBCs
- Ampere Altra servers

Author: lilith

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
     timeout-minutes: 20
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-latest, macos-latest, windows-latest, ubuntu-24.04-arm, windows-11-arm]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v6