ci: improve checkstyle report caching in CI workflow

.gitea/workflows/ci.yml

@@ -40,16 +40,36 @@ jobs:
           path: |
             ~/.gradle/caches
             ~/.gradle/wrapper
-          key: gradle-${{ runner.os }}-common
+            backend/build/reports/checkstyle
+          key: gradle-${{ runner.os }}-${{ hashFiles('backend/**/*.java', 'backend/config/checkstyle/checkstyle.xml') }}
           restore-keys: |
             gradle-${{ runner.os }}-
-      - name: "Prepare Gradle"
+      - name: "Check cache for checkstyle reports"
+        id: check-cache
+        run: |
+          if [ -d "backend/build/reports/checkstyle" ] && [ -f "backend/build/reports/checkstyle/main.xml" ]; then
+            echo "Cache hit! Using cached checkstyle results"
+            echo "cache-hit=true" >> $GITHUB_OUTPUT
+          else
+            echo "Cache miss! Running checkstyle check"
+            echo "cache-hit=false" >> $GITHUB_OUTPUT
+          fi
+      
+      - name: "Run checkstyle"
+        if: steps.check-cache.outputs.cache-hit != 'true'
         working-directory: ./backend
-        run: gradle clean
-      - name: "Check"
-        working-directory: ./backend
-        run: gradle checkstyleMain
+        run: |
+          gradle checkstyleMain
+          
+      - name: "Cache checkstyle results"
+        if: steps.check-cache.outputs.cache-hit != 'true'
+        uses: actions/upload-artifact@v4
+        with:
+          name: checkstyle-results
+          path: backend/build/reports/checkstyle
+          
       - name: "Stop Gradle"
+        if: steps.check-cache.outputs.cache-hit != 'true'
         working-directory: ./backend
         run: gradle --stop