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/tui/src/bottom_pane/textarea.rs

@@ -109,7 +109,7 @@ impl TextArea {
         self.wrapped_lines(width).len() as u16
     }
 
-    #[allow(dead_code)]
+    #[cfg_attr(not(test), allow(dead_code))]
     pub fn cursor_pos(&self, area: Rect) -> Option<(u16, u16)> {
         self.cursor_pos_with_state(area, &TextAreaState::default())
     }
@@ -359,8 +359,9 @@ impl TextArea {
             } => {
                 self.move_cursor_to_end_of_line(true);
             }
-            o => {
-                tracing::debug!("Unhandled key event in TextArea: {:?}", o);
+            _o => {
+                #[cfg(feature = "debug-logs")]
+                tracing::debug!("Unhandled key event in TextArea: {:?}", _o);
             }
         }
     }