fix(userdata): read user data through to the database

The user data cache and the item's in-memory rows were both filled once per
replica and never invalidated, so a pod serving a playback tick read its own
stale resume position and wrote it back over the position another pod had just
saved, silently losing resume points, played state, favourites and ratings.

- drop the user item data cache
- read single and batched user data from the database on every query
- prefetch user data for in-memory sorts and filters so each stays one query
- cover the lost update against real PostgreSQL with two manager instances

MediaBrowser.Controller/Sorting/IUserBaseItemComparer.cs

@@ -1,6 +1,9 @@
 #nullable disable
 
+using System;
+using System.Collections.Generic;
 using Jellyfin.Database.Implementations.Entities;
+using MediaBrowser.Controller.Entities;
 using MediaBrowser.Controller.Library;
 
 namespace MediaBrowser.Controller.Sorting
@@ -27,5 +30,11 @@ namespace MediaBrowser.Controller.Sorting
         /// </summary>
         /// <value>The user data repository.</value>
         IUserDataManager UserDataManager { get; set; }
+
+        /// <summary>
+        /// Gets or sets user data for the items being sorted, keyed by item id, read once up front.
+        /// </summary>
+        /// <value>The prefetched user data, or <c>null</c> when none was prefetched.</value>
+        IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
     }
 }