Cleanup the background task that pauses the SDK when resigning active (#903)

* checking if the stop taskHandle is finished before stopping the bg task

* stopping the sync in background now works properly

* this will prevent the case in which if the app suspends and then is immediately foregrounded again, we do not start the sync

* now works as intended

* code improvement

* improved the code a bit

ElementX/Sources/Services/Client/MockClientProxy.swift

@@ -33,6 +33,8 @@ class MockClientProxy: ClientProxyProtocol {
     var invitesSummaryProvider: RoomSummaryProviderProtocol? = MockRoomSummaryProvider()
 
     var avatarURLPublisher: AnyPublisher<URL?, Never> { Empty().eraseToAnyPublisher() }
+
+    var isSyncing: Bool { false }
     
     internal init(userID: String, roomSummaryProvider: RoomSummaryProviderProtocol? = MockRoomSummaryProvider()) {
         self.userID = userID
@@ -43,6 +45,8 @@ class MockClientProxy: ClientProxyProtocol {
     
     func startSync() { }
     
+    func stopSync(completionHandler: () -> Void) { }
+
     func stopSync() { }
     
     func directRoomForUserID(_ userID: String) async -> Result<String?, ClientProxyError> {