store test [nfc]: Rename stream to channel

Fixes parts of #631

Author: Khader-1

test/model/store_test.dart

@@ -200,17 +200,17 @@ void main() {
     test('smoke', () async {
       final store = eg.store();
       final connection = store.connection as FakeApiConnection;
-      final stream = eg.channel();
+      final channel = eg.channel();
       connection.prepare(json: SendMessageResult(id: 12345).toJson());
       await store.sendMessage(
-        destination: StreamDestination(stream.channelId, 'world'),
+        destination: StreamDestination(channel.channelId, 'world'),
         content: 'hello');
       check(connection.takeLastRequest()).isA<http.Request>()
         ..method.equals('POST')
         ..url.path.equals('/api/v1/messages')
         ..bodyFields.deepEquals({
           'type': 'stream',
-          'to': stream.channelId.toString(),
+          'to': channel.channelId.toString(),
           'topic': 'world',
           'content': 'hello',
           'read_by_sender': 'true',