chore: Add combined mac dylib creation artifact

Author: fuzzybinary

.github/workflows/build.yaml

@@ -42,8 +42,28 @@ jobs:
       - name: Assemble artifacts
         run: dart ./scripts/build_helpers/bin/assemble_artifacts.dart
       - name: 'Upload Artifact'
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: lib-${{ matrix.postfix }}
           path: ./artifacts
-  
+
+  assemble_mac_dylib:
+    runs-on: macos-latest
+    needs: build
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          name: lib-macos-x64
+      - uses: actions/download-artifact@v4
+        with:
+          name: lib-macos-arm64
+      - run: |
+          mkdir -p artifacts/bin
+          mkdir -p artifacts/include
+          lipo lib-macos-x64/bin/libdart_dll.dylib lib-macos-arm64/bin/libdart_dll.dylib -output artifacts/bin/libdart_dll.dylib -create
+          cp -r lib-macos-arm64/include/* artifacts/include
+      - name: 'Upload Artifact'
+        uses: actions/upload-artifact@v4
+        with:
+          name: lib-macos
+          path: ./artifacts