Add Paper A-B performance benchmark

Author: Arbousier1

.github/workflows/benchmark.yml

@@ -0,0 +1,77 @@
+name: A-B Performance Benchmark
+
+on:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  benchmark:
+    name: Paper 26.1.2 A-B benchmark
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Set up Java 25
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: "25"
+
+      - name: Set up Gradle
+        uses: gradle/actions/setup-gradle@v4
+
+      - name: Build disposable benchmark plugin
+        run: ./gradlew benchmarkJar --no-daemon --no-build-cache --rerun-tasks
+
+      - name: Download stable Paper 26.1.2
+        env:
+          PAPER_USER_AGENT: InteractionVisualizer-Benchmark/1.0 (https://github.com/EllanServer/InteractionVisualizer)
+        run: |
+          mkdir -p benchmark-server/plugins
+          BUILDS=$(curl --fail --silent --show-error \
+            -H "User-Agent: $PAPER_USER_AGENT" \
+            https://fill.papermc.io/v3/projects/paper/versions/26.1.2/builds)
+          PAPER_URL=$(echo "$BUILDS" | jq -r 'first(.[] | select(.channel == "STABLE") | .downloads."server:default".url) // empty')
+          test -n "$PAPER_URL"
+          curl --fail --location --show-error \
+            -H "User-Agent: $PAPER_USER_AGENT" \
+            --output benchmark-server/server.jar "$PAPER_URL"
+          cp build/libs/InteractionVisualizer-*-benchmark.jar benchmark-server/plugins/
+
+      - name: Configure isolated benchmark server
+        working-directory: benchmark-server
+        run: |
+          echo 'eula=true' > eula.txt
+          cat > server.properties <<'EOF'
+          online-mode=false
+          level-name=benchmark-world
+          level-type=minecraft:flat
+          generate-structures=false
+          spawn-protection=0
+          view-distance=3
+          simulation-distance=3
+          max-players=1
+          sync-chunk-writes=false
+          EOF
+
+      - name: Run alternating A-B measurements
+        working-directory: benchmark-server
+        run: |
+          java -Xms2G -Xmx2G -XX:+UseG1GC -jar server.jar --nogui | tee benchmark-server.log
+          test -f plugins/InteractionVisualizerBenchmark/benchmark-results.jsonl
+
+      - name: Publish benchmark results
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: interactionvisualizer-ab-${{ github.sha }}
+          path: |
+            benchmark-server/plugins/InteractionVisualizerBenchmark/benchmark-results.jsonl
+            benchmark-server/benchmark-server.log
+          if-no-files-found: warn
+          retention-days: 30