Add SUM Parts reproduction and Seosan Myeongcheon application pipeline

Reproduces the SUM Parts (CVPR 2025) face-labeling benchmark on a single
consumer GPU, then applies it to drone-photogrammetry road survey meshes.

Verified on RTX 3060 12GB / WSL2 Ubuntu 22.04 / CUDA 11.8 / torch 2.0.1:
- CUDA extensions build (pointnet2_batch, pointops, chamfer_dist, emd,
  subsampling)
- PointNet 100 epochs reaches mIoU 17.19, matching the paper's reported 15.1
- OBJ -> PLY conversion round-trips through the model and yields per-point
  predictions

Four upstream source patches, all idempotent, originals preserved:
- numpy aliases removed in 1.24 (np.long etc.) and collections ABCs moved in
  python 3.10
- the blind test split ships label = -1, which crashed ConfusionMatrix
- mode=val referenced `epoch` before assignment

Documents the traps that cost the most time, including VRAM overflow silently
falling back to host RAM on WSL2 (25-100x slowdown, no OOM) and the colour
scale mismatch between r/g/b float32 and red/green/blue uint8.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/check_infer_cfg.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# SUM Parts - did the dataset.test.voxel_max override actually land?
+set -uo pipefail
+
+LOG="${1:-$HOME/sum-parts/runs/coarse_eval/infer.log}"
+
+echo "log: $LOG"
+[ -f "$LOG" ] || { echo "  missing"; exit 1; }
+
+echo
+echo "=== opts line (what was overridden) ==="
+grep -a '^opts:' "$LOG" || echo "  (none)"
+
+echo
+echo "=== dataset block from the cfg dump ==="
+sed -n '/^dataset:/,/^datatransforms:/p' "$LOG" | head -25
+
+echo
+echo "=== how many sub-clouds per tile ==="
+grep -ao 'Test on [0-9]*-th cloud \[[0-9]*\]/\[[0-9]*\]' "$LOG" \
+    | sed 's/.*\///' | sort -u | head
+
+echo
+echo "=== reported metrics ==="
+grep -aE 'test_oa|iou per cls' "$LOG" | tail -4