ci: check performance regressions with CI

refs: https://swiftpackageindex.com/ordo-one/package-benchmark/main/documentation/benchmark/comparingbenchmarksci

.github/workflows/benchmark.yml

@@ -0,0 +1,50 @@
+name: benchmark
+on:
+  pull_request:
+    branches: ["main"]
+jobs:
+  benchmark:
+    runs-on: ubuntu-latest
+    container: swiftlang/swift:nightly-6.0-jammy
+    permissions:
+      pull-requests: write
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install dependencies
+        run: apt-get update && apt-get install --no-install-recommends -y libjemalloc-dev
+      - name: Run benchmarks for PR branch
+        run: swift package --package-path Benchmarks benchmark baseline update pull_request --no-progress --quiet
+      - name: Switch to branch 'main'
+        uses: actions/checkout@v4
+        with:
+          ref: main
+          clean: false
+      - name: Run benchmarks for branch 'main'
+        run: swift package --package-path Benchmarks benchmark baseline update main --no-progress --quiet
+      - name: Compare PR and main
+        id: benchmark
+        run: |
+          echo '## Summary' >> "$GITHUB_STEP_SUMMARY"
+          echo "$(date)" >> "$GITHUB_STEP_SUMMARY"
+          echo "exitStatus=1" >> "$GITHUB_OUTPUT"
+          swift package --package-path Benchmarks benchmark baseline check main pull_request --format markdown >> "$GITHUB_STEP_SUMMARY"
+          echo '---' >> "$GITHUB_STEP_SUMMARY"
+          swift package --package-path Benchmarks benchmark baseline compare main pull_request --no-progress --quiet --format markdown >> "$GITHUB_STEP_SUMMARY"
+          echo "exitStatus=0" >> "$GITHUB_OUTPUT"
+      - name: Pull request comment text
+        id: prtest
+        env:
+          exitStatus: ${{ steps.benchmark.outputs.exitStatus }}
+        run: |
+          echo 'PRTEST<<EOF' >> "$GITHUB_OUTPUT"
+          echo "[Pull request benchmark comparison with 'main' run at $(date -Iseconds)](${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }})" >> "$GITHUB_OUTPUT"
+          [[ $exitStatus == '1' ]] && echo "_Pull request had performance regressions_" >> "$GITHUB_OUTPUT"
+          echo 'EOF' >> "$GITHUB_OUTPUT"
+      - name: Comment PR
+        uses: thollander/actions-comment-pull-request@v3
+        with:
+          message: ${{ steps.prtest.outputs.PRTEST }}
+          comment_tag: execution
+      - name: Exit with correct status
+        run: |
+          exit ${{ steps.benchmark.outputs.exitStatus }}