Use wait_for_event helpers in tests (#4753)

## Summary
- replace manual event polling loops in several core test suites with
the shared wait_for_event helpers
- keep prior assertions intact by using closure captures for stateful
expectations, including plan updates, patch lifecycles, and review flow
checks
- rely on wait_for_event_with_timeout where longer waits are required,
simplifying timeout handling

## Testing
- just fmt


------
https://chatgpt.com/codex/tasks/task_i_68e1d58582d483208febadc5f90dd95e

codex-rs/core/tests/suite/shell_serialization.rs

@@ -17,6 +17,7 @@ use core_test_support::responses::start_mock_server;
 use core_test_support::skip_if_no_network;
 use core_test_support::test_codex::TestCodex;
 use core_test_support::test_codex::test_codex;
+use core_test_support::wait_for_event;
 use serde_json::Value;
 use serde_json::json;
 
@@ -38,12 +39,10 @@ async fn submit_turn(test: &TestCodex, prompt: &str, sandbox_policy: SandboxPoli
         })
         .await?;
 
-    loop {
-        let event = test.codex.next_event().await?;
-        if matches!(event.msg, EventMsg::TaskComplete(_)) {
-            break;
-        }
-    }
+    wait_for_event(&test.codex, |event| {
+        matches!(event, EventMsg::TaskComplete(_))
+    })
+    .await;
 
     Ok(())
 }