Related to #45960
Follow-up to #45961
After #45961 ensured that handleNodeUp is always called for nodes
discovered during rewatchNodes (including stopping nodes), this change
adds a safeguard in ResourceManager.handleNodeUp to skip adding stopping
nodes to resource groups.
1. **resource_manager.go**: Add check for IsStoppingState() in
handleNodeUp to prevent stopping nodes from being added to incomingNode
set and assigned to resource groups.
2. **server.go**:
- Delete processed nodes from sessionMap to avoid duplicate processing
in the subsequent loop
- Add warning logs for stopping state transitions during rewatch
Signed-off-by: Congqi Xia <congqi.xia@zilliz.com>