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 <[email protected]>

src/modules/insert/mod.rs

@@ -16,7 +16,8 @@ pub(crate) mod picker;
 pub mod minsert;
 mod mview_block;
 mod open_obj;
-mod pc_attach;
+pub(crate) mod pc_attach;
+pub(crate) mod pc_crop;
 pub(crate) mod pdf_attach;
 pub(crate) mod pdf_clip;
 pub(crate) mod pdf_import;