nx_geo_hilbert.nx

nx_geo_hilbert.nx -- GEO-005: Hilbert space-filling-curve cell ordering, the S2/H3 superiority target. The geohash (GEO-002) interleaves lon/lat bits = a Z-ORDER (Morton) curve, which has BOUNDARY DISCONTINUITIES: consecutive indices can map to cells far apart (a jump at every quadrant seam), so a range-scan over an index window can miss/overshoot spatially-near cells. The Hilbert curve's DEFINING PROPERTY: consecutive indices are ALWAYS spatially adjacent (Manhattan distance exactly 1) -- no discontinuities. PURE-INTEGER (division/modulo, NO bitwise -- the geohash's no-float discipline + dodges the shift/or miscompile landmine), exact + deterministic. A grid of n=2^order cells per axis maps bijectively to [0, n*n) Hilbert indices. EXCEED is MEASURED, not asserted: hilbert_max_jump==1 vs zorder_max_jump>1 on the SAME grid.