fix: Moves ContextMenu out of core, streamlines code, fixes bugs (#1873)

## Summary
- Removes allocation of a `List<ContextMenuEntry>` every time a context menu is created.
- Moves packet/context menu creation logic out of the core
- Fixes tame entry

## BREAKING CHANGE
> [!Important]
> **Developer Note**
> ```cs
> public virtual void GetContextMenuEntries(Mobile from, List<ContextMenuEntry> list)
> ```
> and similar functions changed to
> ```cs
> public virtual void GetContextMenuEntries(Mobile from, ref PooledRefList<ContextMenuEntry> list)
> ```

Projects/UOContent/Context Menus/OpenBackpackEntry.cs

@@ -0,0 +1,13 @@
+namespace Server.ContextMenus;
+
+public class OpenBackpackEntry : ContextMenuEntry
+{
+    public OpenBackpackEntry() : base(6145)
+    {
+    }
+
+    public override void OnClick(Mobile from, IEntity target)
+    {
+        from.Use(from.Backpack);
+    }
+}