Completer manager tests

Author: hiroshihorie

lib/src/support/completer_manager.dart

@@ -1,5 +1,16 @@
 // Copyright 2025 LiveKit, Inc.
-// A reusable completer manager that handles safe completion and lifecycle management.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
 
 import 'dart:async';