Add tests for the UserSessionStore. (#6065)

* Add enough mock configurations to test the UserSessionStore.

* Add tests for the UserSessionStore.

ElementX/Sources/Mocks/SDK/SyncServiceSDKMock.swift

@@ -0,0 +1,23 @@
+//
+// Copyright 2026 Element Creations Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+// Please see LICENSE files in the repository root for full details.
+//
+
+import Foundation
+import MatrixRustSDK
+import MatrixRustSDKMocks
+
+nonisolated extension SyncServiceSDKMock {
+    struct Configuration {
+        var roomListService = RoomListServiceSDKMock(.init())
+    }
+    
+    convenience init(_ configuration: Configuration) {
+        self.init()
+        
+        roomListServiceReturnValue = configuration.roomListService
+        stateListenerReturnValue = TaskHandleSDKMock()
+    }
+}