Add tests for the UserSessionStore. (#6065)

* Add enough mock configurations to test the UserSessionStore.

* Add tests for the UserSessionStore.

ElementX/Sources/Mocks/SDK/SyncServiceBuilderSDKMock.swift

@@ -0,0 +1,25 @@
+//
+// 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 SyncServiceBuilderSDKMock {
+    struct Configuration {
+        var syncService = SyncServiceSDKMock(.init())
+    }
+    
+    convenience init(_ configuration: Configuration) {
+        self.init()
+        
+        withOfflineModeClosure = { [unowned self] in self }
+        withSharePosEnableClosure = { [unowned self] _ in self }
+        withProfilesExtensionClosure = { [unowned self] in self }
+        finishReturnValue = configuration.syncService
+    }
+}