Re-add markdown streaming (#2029)

Wait for newlines, then render markdown on a line by line basis. Word wrap it for the current terminal size and then spit it out line by line into the UI. Also adds tests and fixes some UI regressions.

codex-rs/core/tests/common/lib.rs

@@ -90,9 +90,11 @@ pub async fn wait_for_event_with_timeout<F>(
 where
     F: FnMut(&codex_core::protocol::EventMsg) -> bool,
 {
+    use tokio::time::Duration;
     use tokio::time::timeout;
     loop {
-        let ev = timeout(wait_time, codex.next_event())
+        // Allow a bit more time to accommodate async startup work (e.g. config IO, tool discovery)
+        let ev = timeout(wait_time.max(Duration::from_secs(5)), codex.next_event())
             .await
             .expect("timeout waiting for event")
             .expect("stream ended unexpectedly");