write a CI workflow for multiple OSes, that compile and test the code using the makefile.

.github/workflows/ci.yaml

@@ -0,0 +1,30 @@
+name: CI
+on:
+  push:
+    branches: [main]
+
+jobs:
+  compile-and-test:
+    strategy:
+      matrix:
+        os:
+          - ubuntu-latest
+          - ubuntu-24.04-arm
+          - windows-latest
+          - windows-11-arm
+          - macos-latest
+    runs-on: ${{matrix.os}}
+    steps:
+      - uses: actions/checkout@v5
+        with:
+          repository: ${{github.repository}}
+          submodules: true
+          fetch-depth: 1
+      - uses: actions/cache@v4
+        with:
+          path: lib/obj/
+          key: ${{runner.os}}-lib/obj-${{github.sha}}
+          restore-keys: ${{runner.os}}-lib/obj-
+      - run: make libs
+      - run: make all
+      - run: make test