fix: integrate with #604

RootDemand gained latency_ms in #604; the Example 2 coverage test's
demand sets it to None (no latency bound).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: zzylol

crates/integration-tests/tests/pass1_sql_coverage.rs

@@ -124,6 +124,7 @@ async fn example2_design_candidates_all_build() {
                 execute_at: None,
             },
             predictability: Predictability::default(),
+            latency_ms: None,
         };
         roots.len()
     ];