Add job for commenting benchmark results on the PR

.github/workflows/pr_benchmarks.yml

@@ -48,7 +48,7 @@ jobs:
           ref: ${{ github.event.pull_request.base.sha }}
           clean: false
 
-      - name: Benchmark baseline and compare
+      - name: Benchmark baseline and generate comparison message
         env:
           RESULTS_NAME: ${{ env.BASE_REF_SHA }}
         run: |
@@ -60,4 +60,55 @@ jobs:
           mv -f results/HEAD results/${{ env.BASE_REF_SHA }}
           
           pip3 install rich
-          ./bench.sh compare ${{ env.BASE_REF_SHA }} ${{ env.HEAD_REF_SHA }}
+          cat > message.md <<EOF
+          # Benchmark results
+          
+          <details>
+          <summary>Benchmarks comparing ${{ github.event.pull_request.base.sha }} and ${{ github.sha }}</summary>
+
+          \`\`\`
+          $(./bench.sh compare ${{ env.BASE_REF_SHA }} ${{ env.HEAD_REF_SHA }})
+          \`\`\`
+
+          </details>
+          EOF
+          
+          cat message.md
+
+      - name: Upload benchmark comparison message
+        uses: actions/upload-artifact@v4
+        with:
+          name: message
+          path: benchmarks/message.md
+
+  comment:
+    name: Post benchmarks in PR comment
+    runs-on: ubuntu-latest
+    needs: [benchmark]
+    permissions:
+      pull-requests: write
+    steps:
+      - name: Download comment message
+        uses: actions/download-artifact@v4
+        with:
+          name: message
+          path: benchmarks
+
+      - name: Print benchmarks
+        run: |
+          cat benchmarks/message.md
+
+      - name: Post a comment
+        uses: actions/github-script@v7
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          script: |
+            const fs = require('fs');
+            const content = fs.readFileSync('benchmarks/message.md', 'utf8');
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: content,
+            })