Improve UI spacing for queued messages (#9162)

Despite good spacing between queued messages and assistant message text:
<img width="462" height="322" alt="Screenshot 2026-01-12 at 4 54 50 PM"
src="https://github.com/user-attachments/assets/e8b46252-0b33-40d2-b431-cb73b9a3bd2e"
/>

Codex has confusing spacing between queued messages and shimmering
status text (making the queued message seem like a sub-item of the
shimmering status text)
<img width="615" height="217" alt="Screenshot 2026-01-12 at 4 54 18 PM"
src="https://github.com/user-attachments/assets/ee5e6095-8fe9-4863-88d2-10472cab8bd6"
/>

This PR changes the spacing between the queued message(s) and shimmering
status text to make it less confusing:
<img width="440" height="240" alt="Screenshot 2026-01-13 at 11 20 36 AM"
src="https://github.com/user-attachments/assets/02dcc690-cbe9-4943-87de-c7300ef51120"
/>

While working on the status/queued spacing change, we noticed two
paste‑burst tests were timing‑sensitive and could fail
on slower CI. We added a small test‑only helper to keep the paste‑burst
state active and refreshed during these tests. This
removes dependence on tight timing and makes the tests deterministic
without affecting runtime behavior.

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__chatwidget_tall.snap

@@ -2,7 +2,9 @@
 source: tui/src/chatwidget/tests.rs
 expression: term.backend().vt100().screen().contents()
 ---
+
 • Working (0s • esc to interrupt)
+
   ↳ Hello, world! 0
   ↳ Hello, world! 1
   ↳ Hello, world! 2
@@ -21,7 +23,6 @@ expression: term.backend().vt100().screen().contents()
   ↳ Hello, world! 15
   ↳ Hello, world! 16
 
-
 › Ask Codex to do anything
 
   100% context left · ? for shortcuts

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__review_queues_user_messages_snapshot.snap

@@ -1,6 +1,5 @@
 ---
 source: tui/src/chatwidget/tests.rs
-assertion_line: 3840
 expression: term.backend().vt100().screen().contents()
 ---
 
@@ -14,10 +13,10 @@ expression: term.backend().vt100().screen().contents()
 
 
 • Working (0s • esc to interrupt)
+
   ↳ Queued while /review is running.
     ⌥ + ↑ edit
 
-
 › Ask Codex to do anything
 
   100% context left · ? for shortcuts