Point clouds: drawn from their scans, placed, cropped and attached as the reference does

Scans (.rcs) and projects (.rcp) are read and their points drawn as
screen-sized dots, coloured by the cloud's stylization. The cloud's
placement carries its scale and rotation; its extents and crops stay in
the scan's coordinates. A missing scan shows the extents with the saved
path. -POINTCLOUDATTACH / POINTCLOUDATTACH, POINTCLOUDCROP and the
POINTCLOUD* settings follow the reference's prompts and messages, the
Properties list is the reference's, and a locked cloud is left alone by
edits.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scene/model/mod.rs

@@ -9,6 +9,7 @@ pub mod ole_pres;
 pub mod pdf_layers;
 pub mod pdf_raster;
 pub mod pdf_vector;
+pub mod point_cloud;
 pub mod underlay_vector;
 pub mod mesh_model;
 pub mod solid_model;