fix: Implement digest calculation loop and update item in DB

src/modes/update.rs

@@ -79,8 +79,25 @@ pub fn mode_update(
         if item_file_metadata.is_ok() {
             debug!("MAIN: Updating stream size of {:?}", item_path);
 
-            // TODO: Add loop here to calculate new digest and put in item.
+            // Create and initialize digest engine
+            let mut digest_engine = digest_engine::get_digest_engine(digest_type);
             
+            // Read file content and update digest
+            let mut file = std::fs::File::open(&item_path)?;
+            let mut buffer = [0; 4096];
+            loop {
+                let bytes_read = file.read(&mut buffer)?;
+                if bytes_read == 0 {
+                    break;
+                }
+                digest_engine.update(&buffer[..bytes_read]);
+            }
+            
+            // Get final digest value
+            let digest_value = digest_engine.finalize()?;
+            
+            // Update item with new digest value
+            item.digest_value = Some(digest_value);
             db::update_item(conn, item.clone())?;
         } else {
             debug!(