burst paste edge cases (#2683)

This PR fixes two edge cases in managing burst paste (mainly on power
shell).
Bugs:
- Needs an event key after paste to render the pasted items

> ChatComposer::flush_paste_burst_if_due() flushes on timeout. Called:
>     - Pre-render in App on TuiEvent::Draw.
>     - Via a delayed frame
>
BottomPane::request_redraw_in(ChatComposer::recommended_paste_flush_delay()).

- Parses two key events separately before starting parsing burst paste

> When threshold is crossed, pull preceding burst chars out of the
textarea and prepend to paste_burst_buffer, then keep buffering.

- Integrates with #2567 to bring image pasting to windows.

codex-rs/tui/src/app.rs

@@ -133,6 +133,12 @@ impl App {
                     self.chat_widget.handle_paste(pasted);
                 }
                 TuiEvent::Draw => {
+                    if self
+                        .chat_widget
+                        .handle_paste_burst_tick(tui.frame_requester())
+                    {
+                        return Ok(true);
+                    }
                     tui.draw(
                         self.chat_widget.desired_height(tui.terminal.size()?.width),
                         |frame| {