Add get_features_in_bbox_grid(layer_id, bbox, *, grid_n=7, step_m=50) to NSPDClient:
delegates grid_n×grid_n WMS GetFeatureInfo calls via NSPDBulkClient.wms_feature_info
(async httpx + Semaphore(3)), deduplicates by feature_id/cad_num/reg_numb_border.
Deprecate get_features_in_bbox (single-pixel, 0-3 results) in docstring — not removed,
used by search_by_quarter (Sub-PR B).
Add classify_engineering_kind(properties) in nspd_denorm.py — regex classifier for
layer 36328 structures: water/sewage/gas/heat/electric/other.
Tests: 31 unit tests (mock-based, no live HTTP), 1 integration skip placeholder.
Foundation only — no behaviour change in harvest_quarter (Sub-PR B).
