fix: Adds Created, LastSerialized, and BeforeSerialize for all entities. (#775)

* Adds `BeforeSerialized` for entities to handle cleanup.
* Adds `Created` and `LastSerialized` fields to all entities. While this is a big bloat, this will be necessary for identifying dangling references to other invalid entities.
* Changes formula for determining a valid reference to be _not null, not deleted, and reference's created date must be at or before the entities last serialized date_.
* Adds versioning to idx file and serializes `Created` and `LastSerialized`.
* Fixes Save Stats and also disables it by default.

Projects/UOContent/Items/Skill Items/Camping/Campfire.cs

@@ -29,7 +29,6 @@ namespace Server.Items
 
             m_Entries = new List<CampfireEntry>();
 
-            Created = Core.Now;
             Timer.StartTimer(TimeSpan.FromSeconds(1.0), TimeSpan.FromSeconds(1.0), OnTick, out _timerToken);
         }
 
@@ -37,9 +36,6 @@ namespace Server.Items
         {
         }
 
-        [CommandProperty(AccessLevel.GameMaster)]
-        public DateTime Created { get; }
-
         [CommandProperty(AccessLevel.GameMaster)]
         public CampfireStatus Status
         {