refactor: 优化 unsubscribe_points_from_source 中 status 锁粒度，使用 get_session 函数

src/connection.rs

@@ -1207,14 +1207,16 @@ impl ConnectionManager {
         }
 
         let target_ids: std::collections::HashSet<Uuid> = point_ids.into_iter().collect();
-        let (session, subscription_id, point_item_pairs) = {
+        let session = self.get_session(source_id).await;
+        let Some(session) = session else {
+            return Ok(0);
+        };
+
+        let (subscription_id, point_item_pairs) = {
             let status = self.status.read().await;
             let Some(conn_status) = status.get(&source_id) else {
                 return Ok(0);
             };
-            let Some(session) = conn_status.session.clone() else {
-                return Ok(0);
-            };
             let Some(subscription_id) = conn_status.subscription_id else {
                 return Ok(0);
             };
@@ -1226,7 +1228,7 @@ impl ConnectionManager {
                 .map(|(point_id, monitored_item_id)| (*point_id, *monitored_item_id))
                 .collect();
 
-            (session, subscription_id, items)
+            (subscription_id, items)
         };
 
         if point_item_pairs.is_empty() {