Coordinate Trace speed training

34/34 correct. PB 3.113s held; session best 3.571s. Reuse: ignore start during scan; keep only signed dx/dy (E/W→dx, N/S→dy) across all 10 moves, compute |dx|+|dy|, add deltas to start once, emit x,y|distance immediately. Stepwise position and 4-direction buckets were slower. Bottleneck: runtime variance + 10-move arithmetic.