Add geometry simplification to polygonize() (#1176)

* Add design spec for polygonize simplification (#1151)

* Add implementation plan for polygonize simplification (#1151)

* Add Douglas-Peucker kernel for polygonize simplification (#1151)

* Add shared-edge simplification orchestrator (#1151)

* Add Visvalingam-Whyatt and wire simplification into polygonize API (#1151)

* Fix degenerate ring handling and add missing test coverage (#1151)

* Add polygonize simplification user guide notebook (#1151)

* Fix column/polygon_points sync on degenerate polygon drop (#1151)

_simplify_polygons now accepts and returns column alongside
polygon_points so both stay in sync when degenerate polygons
are dropped. Added tests for holes, transform, single-pixel
raster, and column/pp length consistency.

Author: brendancol