tools: add llama.cpp comparison baseline + standard benchmark suite

Vendor llama.cpp as a submodule pinned to b9371 and add a one-click
benchmark driver that compares xserv against it on identical workloads:

- setup-llama-cpp.sh: network-optional CUDA build (SM120); convert-to-gguf.sh
  converts the same safetensors to BF16 GGUF for an apples-to-apples baseline.
- tools/bench/: black-box OpenAI-API driver measuring TTFT/TPOT/throughput
  (single-stream + concurrent) and response quality on AIME 2025 + GSM8K.
- fetch_datasets.py pulls datasets to local JSON (GPU host has no network);
  task loaders prefer the local JSON.
- sync-and-build.sh: `bench` subcommand transfers source + datasets to the
  GPU host via tar-over-ssh (no rsync there), builds, and runs the suite.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/bench/fetch_datasets.py

@@ -0,0 +1,40 @@
+"""Pre-fetch quality-benchmark datasets into local JSON.
+
+Run this on a machine WITH network (e.g. your laptop). The resulting
+tools/bench/data/*.json files are then shipped to the GPU host (which has no
+network) by the bench sync step.
+
+Usage:
+  python3 -m tools.bench.fetch_datasets               # all tasks
+  python3 -m tools.bench.fetch_datasets aime2025      # one task
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+
+if __package__ in (None, ""):
+    sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))))
+
+from tools.bench.tasks import aime, gsm8k, save_local
+
+FETCHERS = {
+    "aime2025": aime.load_remote,
+    "gsm8k": gsm8k.load_remote,
+}
+
+
+def main() -> None:
+    wanted = sys.argv[1:] or list(FETCHERS)
+    for name in wanted:
+        if name not in FETCHERS:
+            raise SystemExit(f"unknown task: {name} (have: {', '.join(FETCHERS)})")
+        print(f"[fetch] {name} ...")
+        records = FETCHERS[name]()
+        path = save_local(name, records)
+        print(f"[fetch] {name}: {len(records)} records -> {path}")
+
+
+if __name__ == "__main__":
+    main()