Complete LinkedChildren integration and batch DTO optimizations

This commit integrates remaining performance changes:

- Add batch user data fetching in DtoService to reduce N+1 queries
- Add GetNextUpEpisodesBatch in TVSeriesManager for efficient batch retrieval
- Update Video/Movie/BoxSet to use LibraryManager for alternate versions
- Transition LinkedChild to use ItemId instead of Path (obsolete Path/LibraryItemId)
- Update providers and controllers for LinkedChildren-based references
- Add NextUpEpisodeBatchResult for batched episode queries
- Integrate IDescendantQueryProvider in SqliteDatabaseProvider

Emby.Server.Implementations/Session/SessionManager.cs

@@ -1820,7 +1820,6 @@ namespace Emby.Server.Implementations.Session
                 fields.Remove(ItemFields.Settings);
                 fields.Remove(ItemFields.SortName);
                 fields.Remove(ItemFields.Tags);
-                fields.Remove(ItemFields.ExtraIds);
 
                 dtoOptions.Fields = fields.ToArray();