Revert "Remove some BUI boilerplate" (#30214)

Revert "Remove some BUI boilerplate (#28399)"

This reverts commit cbf329a82d.

Content.Client/Mech/Ui/MechBoundUserInterface.cs

@@ -3,7 +3,6 @@ using Content.Shared.Mech;
 using Content.Shared.Mech.Components;
 using JetBrains.Annotations;
 using Robust.Client.GameObjects;
-using Robust.Client.UserInterface;
 
 namespace Content.Client.Mech.Ui;
 
@@ -21,8 +20,9 @@ public sealed class MechBoundUserInterface : BoundUserInterface
     {
         base.Open();
 
-        _menu = this.CreateWindow<MechMenu>();
-        _menu.SetEntity(Owner);
+        _menu = new(Owner);
+
+        _menu.OnClose += Close;
         _menu.OpenCenteredLeft();
 
         _menu.OnRemoveButtonPressed += uid =>
@@ -60,6 +60,16 @@ public sealed class MechBoundUserInterface : BoundUserInterface
         }
     }
 
+    protected override void Dispose(bool disposing)
+    {
+        base.Dispose(disposing);
+
+        if (!disposing)
+            return;
+
+        _menu?.Close();
+    }
+
     public UIFragment? GetEquipmentUi(EntityUid? uid)
     {
         var component = EntMan.GetComponentOrNull<UIFragmentComponent>(uid);