refactor(feed): 合并首页与剧场频道控制器的重复分桶逻辑

两个控制器的缓存优先、请求序号防串台、分页去重、预取与 seed 完全同构，
此前各写一份。抽出 ChannelFeedController 后，子类只保留分桶 key 与取页
实现；顺带修掉刷新被翻页抢占时 loading 永久为 true 的问题。

test/core/data/services/channel_feed_controller_test.dart

@@ -0,0 +1,50 @@
+// Author: fruit.com.cn
+
+import 'dart:async';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:fruitshorts/core/data/models/drama.dart';
+import 'package:fruitshorts/core/data/models/feed_page.dart';
+import 'package:fruitshorts/core/data/services/channel_feed_controller.dart';
+
+void main() {
+  test('should_clear_loading_when_load_more_supersedes_refresh', () async {
+    final pendingRefresh = Completer<FeedPage>();
+    final controller = _ScriptedFeedController([
+      () async => FeedPage(
+        dramas: [_drama('a')],
+        nextCursor: 'cursor-1',
+        hasMore: true,
+      ),
+      () => pendingRefresh.future,
+      () async => FeedPage(dramas: [_drama('b')], hasMore: false),
+    ]);
+    await controller.refreshCurrent();
+    expect(controller.hasMore, isTrue);
+
+    final refresh = controller.refreshCurrent();
+    final more = controller.loadMore();
+    pendingRefresh.complete(FeedPage(dramas: [_drama('late')], hasMore: false));
+    await Future.wait([refresh, more]);
+
+    // 刷新被翻页抢占后，加载态必须收掉，否则该分桶永远显示加载中且无法再刷新。
+    expect(controller.isLoading, isFalse);
+    expect(controller.loadingMore, isFalse);
+    expect(controller.dramas.map((drama) => drama.id), contains('b'));
+    expect(controller.dramas.map((drama) => drama.id), isNot(contains('late')));
+    controller.dispose();
+  });
+}
+
+class _ScriptedFeedController extends ChannelFeedController<String> {
+  _ScriptedFeedController(this._pages) : super('all');
+
+  final List<Future<FeedPage> Function()> _pages;
+
+  @override
+  Future<FeedPage> fetchPage(String key, {String? cursor}) =>
+      _pages.removeAt(0)();
+}
+
+Drama _drama(String id) =>
+    Drama(id: id, title: id, synopsis: id, posterUrl: '');