Refactor model for strict Clippy checks

crates/model/src/cellmap.rs

@@ -27,7 +27,7 @@ mod tests {
     use gridcraft_core::CellRef;
 
     #[test]
-    fn comments_and_hyperlinks_survive_json() {
+    fn comments_and_hyperlinks_survive_json() -> Result<(), Box<dyn std::error::Error>> {
         let mut s = Sheet::new("S");
         let a1 = CellRef::new(0, 0);
         let c3 = CellRef::new(2, 2);
@@ -45,9 +45,10 @@ mod tests {
             },
         );
         s.hyperlinks.insert(c3, Hyperlink { target: "Sheet1!A1".into(), tooltip: Some("jump".into()), external: false });
-        let json = serde_json::to_string(&s).expect("serialize");
-        let back: Sheet = serde_json::from_str(&json).expect("deserialize");
+        let json = serde_json::to_string(&s)?;
+        let back: Sheet = serde_json::from_str(&json)?;
         assert_eq!(back.comments, s.comments);
         assert_eq!(back.hyperlinks, s.hyperlinks);
+        Ok(())
     }
 }