fix(test): add missing user_id and statement_digest fields in cluster trigger test

Initialize the two fields added to WriteEvent in the audit propagation
work so that the cluster trigger test compiles against the updated type.

Author: farhan-syah

nodedb-cluster-tests/tests/cluster_triggers.rs

@@ -161,6 +161,8 @@ fn event_source_preserved_through_write_event() {
         old_value: None,
         system_time_ms: None,
         valid_time_ms: None,
+        user_id: None,
+        statement_digest: None,
     };
     // After leader failover, new leader's Event Plane replays from WAL.
     // The replayed events have source: User → triggers fire.