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/io/xref_model.rs

@@ -131,7 +131,7 @@ fn root_key(normalized: &str) -> String {
     String::new()
 }
 
-fn is_relative_path(normalized: &str) -> bool {
+pub fn is_relative_path(normalized: &str) -> bool {
     let b = normalized.as_bytes();
     if b.len() >= 2 && b[0].is_ascii_alphabetic() && b[1] == b':' {
         return false;