fix: the bend table and bend lines follow what cut-outs leave of a bend (#607)

The bend table, flat pattern and DXF list a bend only where its centre line has material: a bend that cut-outs (or pockets that together go through the sheet) shorten keeps what is left, and one they split gets a row per piece, all with the bend's number.

Co-authored-by: NOWN-DEV <257771410+NOWN-DEV@users.noreply.github.com>

crates/engine/src/cmd/sheet.rs

@@ -54,7 +54,7 @@ pub static COMMANDS: &[CommandSpec] = &[
         .params("body?, path? → DXF (mm): OUTLINE, BEND_UP and BEND_DOWN (centre lines) layers"),
     CommandSpec::new("sheet.export_bend_table", "Export Bend Table", export_bend_table)
         .noundo()
-        .params("body?, format?: csv|json (default csv), path? → bend table in mm and degrees, including rule and flat centre-line coordinates"),
+        .params("body?, format?: csv|json (default csv), path? → bend table in mm and degrees, including rule and flat centre-line coordinates; a bend that cut-outs split has a row for each piece"),
 ];
 
 fn points(p: &Value, k: &str, cmd: &str) -> Result<Vec<Vec3>> {