ci: add a benchmark workflow

.github/workflows/bench.yml

@@ -0,0 +1,49 @@
+name: Benchstat
+
+on:
+  pull_request:
+    branches: [ master ]
+
+permissions:  # added using https://github.com/step-security/secure-workflows
+  contents: read
+
+jobs:
+
+  bench:
+    name: Performance regression check
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - name: Checkout (previous)
+        uses: actions/checkout@v3
+        with:
+          ref: ${{ github.base_ref }}
+          path: previous
+
+      - name: Checkout (new)
+        uses: actions/checkout@v3
+        with:
+          path: new
+
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version-file: '${{ github.workspace }}/new/go.mod'
+
+      - name: Install dependencies
+        run: go install golang.org/x/perf/cmd/benchstat@latest
+
+      - name: Run Benchmark (previous)
+        timeout-minutes: 5
+        run: |
+          cd previous
+          go test -bench=. -benchmem -benchtime=100ms -count=10 ./... > benchmark.txt
+
+      - name: Run Benchmark (new)
+        timeout-minutes: 5
+        run: |
+          cd new
+          go test -bench=. -benchmem -benchtime=100ms -count=10 ./... > benchmark.txt
+
+      - name: Run Benchstat
+        run: benchstat previous/benchmark.txt new/benchmark.txt