fix(group_sync_worker): add missing Node import in tests

- Added use crate::topology::Node to test imports
- Fixes compilation error: use of undeclared type Node

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/miroir-core/src/group_sync_worker.rs

@@ -382,6 +382,7 @@ mod tests {
     use super::*;
     use crate::group_addition::{GroupAdditionConfig, GroupAdditionCoordinator};
     use crate::scatter::FetchDocumentsResponse;
+    use crate::topology::Node;
     use std::sync::Arc;
 
     // Mock node client for testing