fix(message): make markseen_msgs async compatible

Otherwise this method can not be called from an actually spawned async method, as `PreparedStatement` is `!Send`

src/message.rs

@@ -1417,6 +1417,7 @@ pub async fn markseen_msgs(context: &Context, msg_ids: Vec<MsgId>) -> Result<()>
     }
 
     let conn = context.sql.get_conn().await?;
+    let msgs = async_std::task::spawn_blocking(move || -> Result<_> {
         let mut stmt = conn.prepare_cached(concat!(
             "SELECT",
             "    m.chat_id AS chat_id,",
@@ -1444,6 +1445,9 @@ pub async fn markseen_msgs(context: &Context, msg_ids: Vec<MsgId>) -> Result<()>
         }
         drop(stmt);
         drop(conn);
+        Ok(msgs)
+    })
+    .await?;
 
     let mut updated_chat_ids = BTreeMap::new();