Use simulated time in the long typing test (#39026)

## Why

The 1,000-character human-like typing test waited on the wall clock after
every keypress, making the test unnecessarily slow.

## What changed

Advance an injected timestamp by the recommended paste flush delay and flush
the paste-burst detector explicitly after each character. This preserves the
coverage that slow typing appears directly without creating a paste
placeholder, without sleeping between keypresses.

GitOrigin-RevId: 0c1beb40283f7d73a381cd221725ab4227c8e233

codex-rs/tui/src/bottom_pane/chat_composer.rs

@@ -12190,8 +12190,16 @@ mod tests {
         );
 
         let count = LARGE_PASTE_CHAR_THRESHOLD; // 1000 in current config
-        let chars: Vec<char> = vec!['z'; count];
-        type_chars_humanlike(&mut composer, &chars);
+        let mut now = Instant::now();
+        let step = ChatComposer::recommended_paste_flush_delay();
+        for _ in 0..count {
+            let _ = composer.handle_input_basic_with_time(
+                KeyEvent::new(KeyCode::Char('z'), KeyModifiers::NONE),
+                now,
+            );
+            now += step;
+            let _ = composer.handle_paste_burst_flush(now);
+        }
 
         assert_eq!(composer.draft.textarea.text(), "z".repeat(count));
         assert!(composer.draft.pending_pastes.is_empty());