- Remove client from the list of devices in case registration fails
- Filter other events not related to registration during registration phase
- Cleanup if connect fails
- Reset if after disconnect
- Disconnect callback *after* cleanup is done so object can be deleted

This fixes some of the issues I had like:
- `BLEClient::connect` hangs up and never recovered because registration failed
- `BLEClient` could not be deleted after disconnect or deletion creating ghost events https://github.com/espressif/arduino-esp32/issues/4047
- `BLEClient` could not be properly reused after a connection was attempted (successful or not) 

* Cleanup in case of registration and connect failure.
Cleanup before calling disconnect callback for safe delete.
Reject other events during registration.
Adresses #4047, #4055

* Clear if after unregister #4047