fix: Adds AfterSerialize support. Removes BeforeSerialize support. (#1208)

### Changes
* Implements an AfterSerialize method that is executed synchronously.
* Removes `BeforeSerialize` support since it was dangerous in its current implementation.
* Moves PlayerMobile kill/virtual decay to AfterSerialize.
* Adds kill decay to after Deserialize.

Projects/UOContent/Misc/Guild.cs

@@ -1148,10 +1148,6 @@ namespace Server.Guilds
             list.TrimExcess();
         }
 
-        public override void BeforeSerialize()
-        {
-        }
-
         public override void Serialize(IGenericWriter writer)
         {
             if (LastFealty + TimeSpan.FromDays(1.0) < Core.Now)
@@ -1231,6 +1227,12 @@ namespace Server.Guilds
             writer.Write(Website);
         }
 
+        public override bool ShouldExecuteAfterSerialize => false;
+
+        public override void AfterSerialize()
+        {
+        }
+
         public override void Delete()
         {
             World.RemoveGuild(this);