Cache TUI flex heights across frame passes (#34348)

## Why

Sizing, rendering, and cursor placement can query the same chat widget layout
multiple times in one frame, repeatedly measuring active transcript cells.

## What changed

- Build one chat widget renderable tree per frame and reuse it for sizing,
  rendering, and cursor placement.
- Cache each flex child's desired height by width for the lifetime of that tree.
- Reuse the bottom pane's renderable directly instead of forwarding each
  renderable operation through a wrapper.

## Testing

- Verify flex layouts measure a child once across frame passes and remeasure it
  when the width changes.
- Verify a chat widget frame measures its active transcript cell once.

GitOrigin-RevId: 5ad1a6711f4011c699b5d002b13dc3319cb4db8e

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

@@ -1692,7 +1692,7 @@ impl BottomPane {
         self.as_renderable_with_composer_right_reserve(/*composer_right_reserve*/ 0)
     }
 
-    fn as_renderable_with_composer_right_reserve(
+    pub(crate) fn as_renderable_with_composer_right_reserve(
         &'_ self,
         composer_right_reserve: u16,
     ) -> RenderableItem<'_> {
@@ -1750,43 +1750,6 @@ impl BottomPane {
         }
     }
 
-    pub(crate) fn render_with_composer_right_reserve(
-        &self,
-        area: Rect,
-        buf: &mut Buffer,
-        composer_right_reserve: u16,
-    ) {
-        self.as_renderable_with_composer_right_reserve(composer_right_reserve)
-            .render(area, buf);
-    }
-
-    pub(crate) fn desired_height_with_composer_right_reserve(
-        &self,
-        width: u16,
-        composer_right_reserve: u16,
-    ) -> u16 {
-        self.as_renderable_with_composer_right_reserve(composer_right_reserve)
-            .desired_height(width)
-    }
-
-    pub(crate) fn cursor_pos_with_composer_right_reserve(
-        &self,
-        area: Rect,
-        composer_right_reserve: u16,
-    ) -> Option<(u16, u16)> {
-        self.as_renderable_with_composer_right_reserve(composer_right_reserve)
-            .cursor_pos(area)
-    }
-
-    pub(crate) fn cursor_style_with_composer_right_reserve(
-        &self,
-        area: Rect,
-        composer_right_reserve: u16,
-    ) -> crossterm::cursor::SetCursorStyle {
-        self.as_renderable_with_composer_right_reserve(composer_right_reserve)
-            .cursor_style(area)
-    }
-
     pub(crate) fn set_status_line(&mut self, status_line: Option<Line<'static>>) {
         if self.composer.set_status_line(status_line) {
             self.request_redraw();