store [nfc]: Rename debugStreamStore to debugChannelStore

Fixes parts of #631

Author: Khader-1

lib/model/store.dart

@@ -335,7 +335,7 @@ class PerAccountStore extends ChangeNotifier with ChannelStore, MessageStore {
   final ChannelStoreImpl _channels;
 
   @visibleForTesting
-  ChannelStoreImpl get debugStreamStore => _channels;
+  ChannelStoreImpl get debugChannelStore => _channels;
 
   ////////////////////////////////
   // Messages, and summaries of messages.

test/model/channel_test.dart

@@ -203,8 +203,8 @@ void main() {
       final expectedStore = eg.store(initialSnapshot: eg.initialSnapshot(
         userTopics: expected,
       ));
-      check(store.debugStreamStore.topicVisibility)
-        .deepEquals(expectedStore.debugStreamStore.topicVisibility);
+      check(store.debugChannelStore.topicVisibility)
+        .deepEquals(expectedStore.debugChannelStore.topicVisibility);
     }
 
     test('data structure', () {
@@ -216,7 +216,7 @@ void main() {
           makeUserTopicItem(channel2, 'topic 3', UserTopicVisibilityPolicy.unknown),
           makeUserTopicItem(channel2, 'topic 4', UserTopicVisibilityPolicy.followed),
         ]));
-      check(store.debugStreamStore.topicVisibility).deepEquals({
+      check(store.debugChannelStore.topicVisibility).deepEquals({
         channel1.channelId: {
           'topic 1': UserTopicVisibilityPolicy.muted,
           'topic 2': UserTopicVisibilityPolicy.unmuted,