setup spotless for code formatting

.github/workflows/code-format.yml

@@ -0,0 +1,35 @@
+name: Check code formatting
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+
+jobs:
+  spotless:
+    name: Check Java formatting (Spotless)
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v5
+      - uses: actions/setup-java@v5
+        with:
+          java-version: 17
+          distribution: temurin
+      - uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-
+      - name: Validate Gradle Wrapper
+        uses: gradle/actions/wrapper-validation@v4
+      - name: Check formatting
+        run: ./gradlew spotlessCheck