feat(block-editor): add Test Block preview

Preview the current unsaved block in a disposable drawing with independent history. Keep normal Draw tools available, append Close Test Block, and return to the original editor without saving. Guard persistence paths and handle refresh and parent-close lifecycle by stable document identity.

src/app/commands/inquiry.rs

@@ -614,6 +614,8 @@ impl OpenCADStudio {
             "BSAVE" => {
                 self.save_block_edit(i);
             }
+            "BTESTBLOCK" => return Some(self.open_block_test(i)),
+            "BCLOSETESTBLOCK" => return Some(self.close_block_test(i)),
             "BSAVEAS" => {
                 self.open_block_save_as_dialog(i);
             }