Implement newsreader counting

server/src/nm.rs

@@ -41,6 +41,10 @@ pub fn threadset_to_messages(thread_set: notmuch::ThreadSet) -> Result<Vec<Messa
     Ok(Vec::new())
 }
 
+pub async fn count(nm: &Notmuch, query: &str) -> Result<usize, ServerError> {
+    Ok(nm.count(query)?)
+}
+
 pub async fn search(
     nm: &Notmuch,
     after: Option<String>,