Plot: redraw PlotDate hosts inside blocks and attributes

A plot stamps PlotDate fields, but the redraw only dropped the host's
own tessellation: an attribute is drawn by its INSERT and a host inside
a block definition by every reference to the block, so both still
showed the old value on screen and in the plotted output. The changed
hosts now redraw through their INSERT / the block's references (block
cache refreshed), without re-tessellating anything else. The codec is
patched to the field format code fixes.

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

src/app/update/file.rs

@@ -3771,8 +3771,7 @@ impl OpenCADStudio {
         let i = self.active_tab;
         let hosts = crate::entities::field::stamp_plot_fields(&mut self.tabs[i].scene.document);
         if !hosts.is_empty() {
-            let changes: Vec<_> = hosts.into_iter().map(|h| (h, crate::scene::ChangeKind::Modified)).collect();
-            self.tabs[i].scene.bump_entities(&changes);
+            self.tabs[i].scene.bump_text_hosts(&hosts);
             self.tabs[i].dirty = true;
         }
     }