Add comprehensive ANN benchmarking suite (#279)

Extend benchmarks-ann/ with results database (SQLite with per-query detail
and continuous writes), dataset subfolder organization, --subset-size and
--warmup options. Supports systematic comparison across flat, rescore, IVF,
and DiskANN index types.

benchmarks-ann/datasets/nyt/build-contents.py

@@ -0,0 +1,52 @@
+# /// script
+# requires-python = ">=3.12"
+# dependencies = [
+#     "duckdb",
+# ]
+# ///
+
+import argparse
+import os
+import sqlite3
+import duckdb
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Load NYT headline CSVs into a SQLite contents database via DuckDB",
+    )
+    parser.add_argument(
+        "--data-dir", "-d", default="data",
+        help="Directory containing NYT CSV files (default: data)",
+    )
+    parser.add_argument(
+        "--output", "-o", required=True,
+        help="Path to the output SQLite database",
+    )
+    args = parser.parse_args()
+
+    glob_pattern = os.path.join(args.data_dir, "new_york_times_stories_*.csv")
+
+    con = duckdb.connect()
+    rows = con.execute(
+        f"""
+        SELECT
+            row_number() OVER () AS id,
+            headline
+        FROM read_csv('{glob_pattern}', auto_detect=true, union_by_name=true)
+        WHERE headline IS NOT NULL AND headline != ''
+        """
+    ).fetchall()
+    con.close()
+
+    db = sqlite3.connect(args.output)
+    db.execute("CREATE TABLE contents(id INTEGER PRIMARY KEY, headline TEXT)")
+    db.executemany("INSERT INTO contents VALUES (?, ?)", rows)
+    db.commit()
+    db.close()
+
+    print(f"Wrote {len(rows)} headlines to {args.output}")
+
+
+if __name__ == "__main__":
+    main()