doc: update documentation to reach higher coverage

01.workspace/heave/src/imp/catalog_len.rs

@@ -1,6 +1,16 @@
 use crate::*;
 
 impl Catalog {
+    /// Returns the number of entities in the catalog.
+    ///
+    /// # Returns
+    ///
+    /// The total number of entities currently held in the catalog's memory.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(FailedTo::LockCatalog)` if the catalog's internal mutex
+    /// could not be locked.
     pub fn len(&self) -> Result<usize, FailedTo> {
         self.with_items(|items| Ok(items.len()))
     }