Report teardown once at CLOSE_EVT and refuse connects on a busy slot

tests/components/ble_device_base/test_gatt_client_contract.cpp

@@ -51,6 +51,9 @@ class MinimalConnection {
   }
   GattServiceTable get_service_table() { return {}; }
   void release_services() {}
+  bool disconnect_pending() const { return false; }
+  void cancel_pending_disconnect() {}
+  void set_connection_type(ConnectionType ct) {}
 
  protected:
   RecordingSink *listener_{nullptr};