refactor(subscribe): unify best_version episode upgrade logic and always track downloads in note

- Simplify and centralize logic for filtering TV episodes during best_version (wash) mode, ensuring only episodes with strictly higher priority are considered for upgrade.
- Always update subscribe.note with downloaded episodes regardless of best_version state, ensuring download history is reliably tracked and available for all subscription modes.
- Remove redundant episode_group field from subscribe dict output.
- Refactor search: remove multi-page search logic, streamline concurrent site search for both sync and async paths, and update progress reporting accordingly.
- Remove obsolete tests for allowed_episodes propagation and note tracking, as logic is now unified and simplified.

app/chain/search.py

@@ -882,7 +882,6 @@ class SearchChain(ChainBase):
 
         # 开始匹配
         _match_torrents = []
-        torrenthelper = TorrentHelper()
         try:
             # 英文标题应该在别名/原标题中，不需要再匹配
             logger.info(f"开始匹配结果 标题：{mediainfo.title}，原标题：{mediainfo.original_title}，别名：{mediainfo.names}")
@@ -916,7 +915,7 @@ class SearchChain(ChainBase):
                     continue
 
                 # 比对种子
-                if torrenthelper.match_torrent(mediainfo=mediainfo,
+                if TorrentHelper.match_torrent(mediainfo=mediainfo,
                                                torrent_meta=torrent_meta,
                                                torrent=torrent):
                     # 匹配成功
@@ -950,7 +949,7 @@ class SearchChain(ChainBase):
         # 排序
         progress.update(value=99,
                         text=f'正在对 {len(contexts)} 个资源进行排序，请稍候...')
-        contexts = torrenthelper.sort_torrents(contexts)
+        contexts = TorrentHelper.sort_torrents(contexts)
 
         # 结束进度
         logger.info(f'搜索完成，共 {len(contexts)} 个资源')

app/chain/subscribe.py

@@ -1441,7 +1441,7 @@ class SubscribeChain(ChainBase):
                                     not torrent_mediainfo.tmdb_id and not torrent_mediainfo.douban_id):
                                 logger.debug(
                                     f'{torrent_info.site_name} - {torrent_info.title} 重新识别失败，尝试通过标题匹配...')
-                                if torrenthelper.match_torrent(mediainfo=mediainfo,
+                                if TorrentHelper.match_torrent(mediainfo=mediainfo,
                                                                torrent_meta=torrent_meta,
                                                                torrent=torrent_info):
                                     # 匹配成功