fix: debounce resize and enlarge broadcast buffer for TUI resize stability

desktop/integration_test/e2e_test.dart

@@ -5,7 +5,6 @@
 //
 // 运行前需先启动 Rust 服务端（cd .. && cargo run）。
 // 运行：flutter test integration_test -d windows
-import 'dart:async';
 import 'dart:typed_data';
 
 import 'package:flutter/foundation.dart';
@@ -74,7 +73,7 @@ String _gridText(TerminalEngine engine) {
   final sb = StringBuffer();
   for (var r = 0; r < grid.rows; r++) {
     for (var c = 0; c < grid.columns; c++) {
-      final cp = grid.codepointAt(r, c) as int;
+      final cp = grid.codepointAt(r, c);
       sb.writeCharCode(cp == 0 ? 32 : cp);
     }
     sb.write('\n');