P9 (WIP): compiled kernels (rust/simurg-core, PyO3) with bit-identical pure-Python fallback

Rust ports of the hot paths found by profiling: fused per-locus GenCall calling
and scoring, BAF/LRR, libm maps with CPython math semantics, both nearest-neighbour
searches of the normalization fit, and the BPM LocusEntry parser. Address
coverage is memoised per IDAT layout. SIMURG_PURE_PYTHON=1 forces the pure paths.
On the Pi: genotype_sample 3.4 s -> 1.1 s, 36-sample GSA run 131 s -> 46 s, BPM
read 4x faster; 36 GSA + 6 Omni2.5 GTCs and QC tables byte-identical to the pure
path; tests/unit/test_core_kernels.py checks every kernel on edge cases.
bench/profile_genotype.py, bench/scaling.py, cloud task p9 (thread scaling).

bench/scaling.py

@@ -0,0 +1,109 @@
+#!/usr/bin/env python3
+"""Thread scaling of ``simurg genotype`` (plan §18 P9 gate: ≥ 20 samples/min/core on GSA-size arrays, linear
+scaling to 32 threads).
+
+For every worker count the same N samples are genotyped (``--no-cohort-qc``); the per-sample phase is timed from
+the run log ("genotyping … sample(s)" → "done"), so manifest loading is reported separately and does not blur
+the scaling. Writes a JSON summary.
+
+    python bench/scaling.py --bpm M.bpm --egt C.egt --idats DIR --out OUT --threads 1,2,4,8 [--samples N]
+"""
+
+from __future__ import annotations
+
+import argparse
+import datetime as dt
+import json
+import os
+import subprocess
+import sys
+import time
+from pathlib import Path
+
+
+def phase_seconds(log: Path) -> tuple[float, float]:
+    """(manifest+setup seconds, per-sample phase seconds) from a genotype run log."""
+    ts: dict[str, dt.datetime] = {}
+    for line in log.read_text().splitlines():
+        rec = json.loads(line)
+        msg = rec.get("msg") or ""
+        t = dt.datetime.fromisoformat(rec["ts"].replace("Z", "+00:00"))
+        ts.setdefault("first", t)
+        if msg.startswith("genotyping "):
+            ts["start"] = t
+        elif msg.startswith("done:"):
+            ts["done"] = t
+    return (ts["start"] - ts["first"]).total_seconds(), (ts["done"] - ts["start"]).total_seconds()
+
+
+def subset(idats: Path, n: int, dest: Path) -> Path:
+    grn = sorted(p for p in idats.rglob("*_Grn.idat*"))
+    if n <= 0 or n >= len(grn):
+        return idats
+    dest.mkdir(parents=True, exist_ok=True)
+    for g in grn[:n]:
+        d = dest / g.parent.name
+        d.mkdir(exist_ok=True)
+        for p in (g, g.with_name(g.name.replace("_Grn.", "_Red."))):
+            link = d / p.name
+            if not link.exists():
+                link.symlink_to(p.resolve())
+    return dest
+
+
+def main() -> int:
+    ap = argparse.ArgumentParser(description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+    ap.add_argument("--bpm", required=True)
+    ap.add_argument("--egt", required=True)
+    ap.add_argument("--idats", required=True, type=Path)
+    ap.add_argument("--out", required=True, type=Path)
+    ap.add_argument("--threads", default="1,2,4")
+    ap.add_argument("--samples", type=int, default=0, help="use the first N samples (0 = all)")
+    ap.add_argument("--simurg", default=str(Path(sys.executable).with_name("simurg")))
+    ap.add_argument("--pure-python", action="store_true", help="run with SIMURG_PURE_PYTHON=1")
+    a = ap.parse_args()
+    a.out.mkdir(parents=True, exist_ok=True)
+    idats = subset(a.idats, a.samples, a.out / "idats")
+    n = len(list(idats.rglob("*_Grn.idat*")))
+    env = {**os.environ, "SIMURG_PURE_PYTHON": "1" if a.pure_python else "0"}
+    runs = []
+    for t in (int(x) for x in a.threads.split(",")):
+        out = a.out / f"t{t}"
+        t0 = time.time()
+        cmd = [a.simurg, "genotype", "--bpm", a.bpm, "--egt", a.egt, "--idats", str(idats), "--out", str(out),
+               "--threads", str(t), "--no-cohort-qc", "--autocall-date", "1/1/2026 12:00:00 AM",
+               "--quiet", "--force"]  # fmt: skip
+        rc = subprocess.run(cmd, env=env).returncode
+        wall = time.time() - t0
+        setup, phase = phase_seconds(out / "logs" / "genotype.log")
+        runs.append(
+            {
+                "threads": t,
+                "rc": rc,
+                "wall_s": round(wall, 1),
+                "setup_s": round(setup, 1),
+                "per_sample_phase_s": round(phase, 2),
+                "samples_per_min": round(60 * n / phase, 1) if phase else None,
+                "samples_per_min_per_core": round(60 * n / phase / t, 1) if phase else None,
+            }
+        )
+        print(json.dumps(runs[-1]), flush=True)
+    base = runs[0]["per_sample_phase_s"] * runs[0]["threads"]
+    for r in runs:
+        r["speedup_vs_first"] = round(base / r["per_sample_phase_s"], 2) if r["per_sample_phase_s"] else None
+        r["efficiency"] = round(r["speedup_vs_first"] / r["threads"], 3) if r["speedup_vs_first"] else None
+    from simurg._core import backend
+
+    summary = {
+        "samples": n,
+        "backend": "python" if a.pure_python else backend(),
+        "cpu_count": os.cpu_count(),
+        "machine": os.uname().machine,
+        "runs": runs,
+    }
+    (a.out / "scaling.json").write_text(json.dumps(summary, indent=1))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())