ci: add benchmark workflow

.github/scripts/aggregate_benchmarks.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+"""Aggregate benchmark JSON files by taking the median across runner attempts."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import statistics
+from pathlib import Path
+
+from compare_benchmarks import Benchmark, extract_benchmarks
+
+
+def collect_benchmarks(paths: list[Path]) -> dict[str, list[Benchmark]]:
+    collected: dict[str, list[Benchmark]] = {}
+    for path in paths:
+        for name, benchmark in extract_benchmarks(path).items():
+            collected.setdefault(name, []).append(benchmark)
+    return collected
+
+
+def aggregate(collected: dict[str, list[Benchmark]]) -> dict[str, dict[str, object]]:
+    aggregated: dict[str, dict[str, object]] = {}
+    for name, benchmarks in sorted(collected.items()):
+        values = [benchmark.value for benchmark in benchmarks]
+        unit = next((benchmark.unit for benchmark in benchmarks if benchmark.unit), "")
+        metric = next((benchmark.metric for benchmark in benchmarks if benchmark.metric), "value")
+        aggregated[name] = {
+            "value": statistics.median(values),
+            "unit": unit,
+            "metric": f"median-of-attempt-{metric}",
+            "attempts": len(values),
+            "attempt_values": values,
+        }
+    return aggregated
+
+
+def main_from_paths(input_dir: Path, output: Path) -> int:
+    paths = sorted(input_dir.rglob("*.json"))
+    if not paths:
+        raise ValueError(f"No benchmark JSON files found in {input_dir}")
+
+    output.parent.mkdir(parents=True, exist_ok=True)
+    output.write_text(
+        json.dumps(aggregate(collect_benchmarks(paths)), indent=2, sort_keys=True) + "\n",
+        encoding="utf-8",
+    )
+    return 0
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--input-dir", required=True, type=Path)
+    parser.add_argument("--output", required=True, type=Path)
+    args = parser.parse_args()
+    return main_from_paths(input_dir=args.input_dir, output=args.output)
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())