ci(GitHub): add benchmark action

Author: userzimmermann

.github/workflows/benchmark.yml

@@ -0,0 +1,72 @@
+name: Benchmark
+
+on:
+  push:
+  pull_request:
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  benchmark:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+
+    - name: Setup Go environment
+      uses: actions/setup-go@v4
+      with:
+        go-version: 1.25.1
+
+    - name: Install benchstat
+      run: go install golang.org/x/perf/cmd/benchstat@latest
+
+    - name: Run benchmarks on base branch
+      if: github.event_name == 'pull_request'
+      run: |
+        git checkout ${{ github.event.pull_request.base.sha }}
+        go mod tidy
+        go test -bench . -count 7 -benchmem > base-bench.txt
+        git checkout ${{ github.event.pull_request.head.sha }}
+
+    - name: Run benchmarks on current commit
+      run: |
+        go mod tidy
+        go test -bench . -count 7 -benchmem > current-bench.txt
+
+    - name: Compare benchmarks
+      if: github.event_name == 'pull_request'
+      run: |
+        cat > benchmark-comment.md << EOF
+        ## Benchmark Results
+
+        \`\`\`
+        $(benchstat base-bench.txt current-bench.txt || echo "No significant differences found.")
+        \`\`\`
+        EOF
+
+    - name: Comment PR with benchmark results
+      if: github.event_name == 'pull_request'
+      uses: actions/github-script@v6
+      with:
+        script: |
+          const fs = require('fs');
+          const comment = fs.readFileSync('benchmark-comment.md', 'utf8');
+          github.rest.issues.createComment({
+            issue_number: context.issue.number,
+            owner: context.repo.owner,
+            repo: context.repo.repo,
+            body: comment
+          });
+
+    - name: Check for significant regressions
+      if: github.event_name == 'pull_request'
+      run: |
+        # Parse benchstat output for significant regressions
+        if benchstat base-bench.txt current-bench.txt | grep -E '\+[0-9]+\.[0-9]+%.*p=0\.[0-9]+' | grep -v '~'; then
+          echo "::warning::Potential performance regression detected. Review benchmark results."
+        fi