Attempt to fix unified_exec_formats_large_output_summary flakiness (#7029)

second attempt to fix this test after
https://github.com/openai/codex/pull/6884. I think this flakiness is
happening because yield_time is too small for a 10,000 step loop in
python.

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

@@ -1622,8 +1622,8 @@ async fn unified_exec_formats_large_output_summary() -> Result<()> {
     } = builder.build(&server).await?;
 
     let script = r#"python3 - <<'PY'
-for i in range(10000):
-    print("token token ")
+import sys
+sys.stdout.write("token token \n" * 5000)
 PY
 "#;