layout/tests: Make UpdateConfig an actual Op

We can do it now that it's non-Copy. This also fixes a new stack
overflow when running the random test in debug mode (which somehow
occurs even though it's skipped in debug mode) that appeared after
adding LayoutPart for some unbeknownst to me reason.

src/layout/tests.rs

@@ -723,6 +723,10 @@ enum Op {
         window: usize,
     },
     ToggleOverview,
+    UpdateConfig {
+        #[proptest(strategy = "arbitrary_layout_part().prop_map(Box::new)")]
+        layout_config: Box<niri_config::LayoutPart>,
+    },
 }
 
 impl Op {
@@ -1546,6 +1550,14 @@ impl Op {
             Op::ToggleOverview => {
                 layout.toggle_overview();
             }
+            Op::UpdateConfig { layout_config } => {
+                let options = Options {
+                    layout: niri_config::Layout::from_part(&layout_config),
+                    ..Default::default()
+                };
+
+                layout.update_options(options);
+            }
         }
     }
 }
@@ -3558,7 +3570,6 @@ proptest! {
     fn random_operations_dont_panic(
         ops: Vec<Op>,
         layout_config in arbitrary_layout_part(),
-        post_layout_config in prop::option::of(arbitrary_layout_part()),
     ) {
         // eprintln!("{ops:?}");
         let options = Options {
@@ -3566,15 +3577,6 @@ proptest! {
             ..Default::default()
         };
 
-        let mut layout = check_ops_with_options(options, ops);
-
-        if let Some(layout_config) = post_layout_config {
-            let post_options = Options {
-                layout: niri_config::Layout::from_part(&layout_config),
-                ..Default::default()
-            };
-            layout.update_options(post_options);
-            layout.verify_invariants();
-        }
+        check_ops_with_options(options, ops);
     }
 }