Fix: Add .serialized to test suites that mutate EnvironmentStorage.active

Minimize race window in FocusState requestFocus test by tightening the
EnvironmentStorage.active scope. Add .serialized to Button Tests and
StatusBarItems Modifier Tests suites.

Tests/TUIkitTests/ButtonTests.swift

@@ -95,7 +95,7 @@ struct ButtonStyleTests {
 
 // MARK: - Button Tests
 
-@Suite("Button Tests")
+@Suite("Button Tests", .serialized)
 struct ButtonTests {
 
     @Test("Button can be created with label and action")

Tests/TUIkitTests/FocusTests.swift

@@ -345,13 +345,14 @@ struct FocusStateTests {
         EnvironmentStorage.active.reset()
     }
 
-    @Test("FocusState requestFocus works")
+    @Test("FocusState requestFocus changes focus via environment manager")
     func focusStateRequestFocus() {
-        // Set up a focus manager in the environment
+        // Set up a dedicated focus manager in the environment.
+        // Note: FocusState.requestFocus() reads from EnvironmentStorage.active,
+        // so we must set it and verify in one uninterrupted sequence.
         let manager = FocusManager()
         var environment = EnvironmentValues()
         environment.focusManager = manager
-        EnvironmentStorage.active.environment = environment
 
         let element1 = MockFocusable(id: "req-1")
         let element2 = MockFocusable(id: "req-2")
@@ -359,13 +360,18 @@ struct FocusStateTests {
         manager.register(element1)
         manager.register(element2)
 
-        let state = FocusState(id: "req-2")
-        state.requestFocus()
+        // First element is focused after registration
+        #expect(manager.isFocused(id: "req-1"))
 
-        #expect(manager.isFocused(id: "req-2"))
-
-        // Cleanup
+        // Set environment, request focus, and verify — all within the
+        // EnvironmentStorage scope to minimize the race window with
+        // other test suites that also mutate EnvironmentStorage.active.
+        EnvironmentStorage.active.environment = environment
+        FocusState(id: "req-2").requestFocus()
+        let focusedReq2 = manager.isFocused(id: "req-2")
         EnvironmentStorage.active.reset()
+
+        #expect(focusedReq2, "req-2 should be focused after requestFocus()")
     }
 }
 

Tests/TUIkitTests/StatusBarTests.swift

@@ -817,7 +817,7 @@ struct StatusBarItemBuilderTests {
 
 // MARK: - StatusBarItems Modifier Tests
 
-@Suite("StatusBarItems Modifier Tests")
+@Suite("StatusBarItems Modifier Tests", .serialized)
 struct StatusBarItemsModifierTests {
 
     @Test("statusBarItems modifier sets items in environment")