ci: add GitHub Actions macOS workflow to build & run tests

Author: linhay

.github/workflows/ci.yml

@@ -0,0 +1,45 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build-and-test:
+    name: Build & Test (macOS)
+    runs-on: macos-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Swift version
+        run: swift --version
+
+      - name: Cache SwiftPM
+        uses: actions/cache@v4
+        with:
+          path: |
+            .build
+            .swiftpm
+          key: ${{ runner.os }}-swift-${{ hashFiles('Package.resolved') }}
+          restore-keys: |
+            ${{ runner.os }}-swift-
+
+      - name: Resolve packages
+        run: swift package resolve
+
+      - name: Build (debug)
+        run: swift build
+
+      - name: Run tests (verbose)
+        run: swift test --parallel
+
+      - name: List package structure
+        if: failure()
+        run: |
+          echo "-- ls -la --"
+          ls -la
+          echo "-- swift package show-dependencies --"
+          swift package show-dependencies --format json || true