perf: optimize token streaming with balanced approach (#635)

- Replace setTimeout(10ms) with queueMicrotask for immediate processing
- Add minimal 3ms setTimeout for rendering to maintain readable UX
- Reduces per-token delay while preserving streaming experience
- Add performance test to verify optimization works correctly

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Thibault Sottiaux <tibo@openai.com>

codex-cli/tests/history-overlay.test.tsx

@@ -60,7 +60,7 @@ function createFunctionCall(
     id: `fn_${Math.random().toString(36).slice(2)}`,
     call_id: `call_${Math.random().toString(36).slice(2)}`,
     arguments: JSON.stringify(args),
-  };
+  } as ResponseFunctionToolCallItem;
 }
 
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