fix(core): Adds SkipLocalsInitAttribute support, optimizes broadcasted packets (#363)

- [X] Adds support for `SkipLocalsInitAttribute`. SkipLocalsInitAttribute skips initializing stack variables including `stackalloc`. I don't think it is wired/working yet but should be implemented soon.
- [X] Optimizes broadcasted packets by checking if the first byte (packet ID) is non-zero. If it is already set, it reuses the buffer.
- [X] Removes unnecessary refs to Spans. I don't think the Span struct itself is mutable, so a ref is not helpful.

Projects/UOContent/Commands/VisibilityList.cs

@@ -70,7 +70,7 @@ namespace Server.Commands
                 if (list.Count > 0)
                 {
                     Span<byte> removeEntity = stackalloc byte[OutgoingEntityPackets.RemoveEntityLength];
-                    OutgoingEntityPackets.CreateRemoveEntity(ref removeEntity, pm.Serial);
+                    removeEntity.InitializePacket();
 
                     for (var i = 0; i < list.Count; ++i)
                     {
@@ -78,6 +78,11 @@ namespace Server.Commands
 
                         if (!m.CanSee(pm) && Utility.InUpdateRange(m, pm))
                         {
+                            if (removeEntity[0] == 0)
+                            {
+                                OutgoingEntityPackets.CreateRemoveEntity(removeEntity, pm.Serial);
+                            }
+
                             m.NetState?.Send(removeEntity);
                         }
                     }