P9 complete: compiled kernels validated (byte-identical, 78-80 GSA samples/min/core), scaling report

Graviton3 c7g.8xlarge, 360 GSE165845 arrays: 360/360 GTCs identical between the Rust
kernels and the pure-Python paths; 1 worker 78-80 samples/min (pure Python 29.6).
Scaling 1->8 workers efficiency 0.87-0.90; above that the 125 MB/s gp3 disk caps the
run (~620 samples/min) and, on a RAM disk, a fixed per-worker start-up cost limits a
360-sample batch to efficiency 0.48 at 32 workers (K-025). Worker state is pickled once.
docs/validation/P9.md, result JSONs, guide/README/CHANGELOG updates.

docs/validation/P9_scaling_ramdisk.json

@@ -0,0 +1,74 @@
+{
+ "samples": 360,
+ "backend": "rust 1.0.0",
+ "cpu_count": 32,
+ "machine": "aarch64",
+ "runs": [
+  {
+   "threads": 1,
+   "rc": 0,
+   "wall_s": 292.6,
+   "setup_s": 6.8,
+   "per_sample_phase_s": 270.27,
+   "samples_per_min": 79.9,
+   "samples_per_min_per_core": 79.9,
+   "speedup_vs_first": 1.0,
+   "efficiency": 1.0
+  },
+  {
+   "threads": 4,
+   "rc": 0,
+   "wall_s": 93.3,
+   "setup_s": 6.8,
+   "per_sample_phase_s": 70.94,
+   "samples_per_min": 304.5,
+   "samples_per_min_per_core": 76.1,
+   "speedup_vs_first": 3.81,
+   "efficiency": 0.953
+  },
+  {
+   "threads": 8,
+   "rc": 0,
+   "wall_s": 59.7,
+   "setup_s": 6.8,
+   "per_sample_phase_s": 37.37,
+   "samples_per_min": 578.0,
+   "samples_per_min_per_core": 72.2,
+   "speedup_vs_first": 7.23,
+   "efficiency": 0.904
+  },
+  {
+   "threads": 16,
+   "rc": 0,
+   "wall_s": 44.4,
+   "setup_s": 6.8,
+   "per_sample_phase_s": 22.06,
+   "samples_per_min": 979.3,
+   "samples_per_min_per_core": 61.2,
+   "speedup_vs_first": 12.25,
+   "efficiency": 0.766
+  },
+  {
+   "threads": 24,
+   "rc": 0,
+   "wall_s": 40.6,
+   "setup_s": 6.8,
+   "per_sample_phase_s": 18.22,
+   "samples_per_min": 1185.6,
+   "samples_per_min_per_core": 49.4,
+   "speedup_vs_first": 14.83,
+   "efficiency": 0.618
+  },
+  {
+   "threads": 32,
+   "rc": 0,
+   "wall_s": 40.0,
+   "setup_s": 6.8,
+   "per_sample_phase_s": 17.62,
+   "samples_per_min": 1225.7,
+   "samples_per_min_per_core": 38.3,
+   "speedup_vs_first": 15.34,
+   "efficiency": 0.479
+  }
+ ]
+}