feat: upate darts

cli_sample/lib/cli_sample.dart

@@ -1,3 +1,16 @@
-int calculate() {
-  return 6 * 7;
+import 'dart:math';
+
+int power() {
+  return pow(2, 10);
+}
+
+Future<void> sleep(int secs) async {
+  await Future.delayed(Duration(seconds: secs));
+}
+
+Stream<String> get_names() async* {
+  await sleep(1);
+  yield 'aaaa';
+  await sleep(1);
+  yield 'bbbb';
 }