Refactor client update handling to support nullable parameters for name and expiration

- Updated the `UpdateClientAsync` method in `IXuiPanelGateway` to accept nullable parameters for `name` and `expiresAt`, allowing for more flexible client management without unintended modifications.
- Adjusted the `BlockUserCommandHandler`, `UnblockUserCommandHandler`, and other related command handlers to utilize the new nullable parameters, ensuring that client names remain unchanged during block/unblock operations and that expiration dates are managed correctly.
- Enhanced the billing and configuration handling to reflect the new logic for managing client states based on expiration rather than enabling/disabling, improving reliability in client status management.
- Updated tests to cover the new behavior and ensure proper functionality across the application.

backend/src/PnvPanel.Application/Billing/BillingConfigResumer.cs

@@ -47,13 +47,18 @@ internal static class BillingConfigResumer
 
                 if (inbound is not null && node is not null)
                 {
+                    // Возвращаем через expiryTime = новый newPaidUntil, а не enable:true — тот же
+                    // механизм приостановки, что и у BillingService (см. IXuiPanelGateway.UpdateClientAsync):
+                    // переписываем просроченную дату на настоящую, панель/Xray сами перестают считать
+                    // клиента истёкшим. name: null — не переименовываем клиента.
                     var updateResult = await gateway.UpdateClientAsync(
                         node,
                         inbound.RemoteInboundId,
                         config.ClientExternalId,
                         config.Protocol,
-                        config.Label ?? config.ClientEmail,
-                        enable: true,
+                        name: null,
+                        enable: null,
+                        expiresAt: newPaidUntil,
                         cancellationToken
                     );