feat: Add diagnostics library for tracking stats/counters

Add a generic library that can be used to track counters, or elapsed time (e.g. how long it takes on average to connect to mqtt).  This is a copy of https://github.com/allenporter/python-google-nest-sdm/blob/main/google_nest_sdm/diagnostics.py

This is an initial pass to add a few initial example metrics for MQTT, but we can add more as we need fine grained details in diagnostics.

Author: allenporter

roborock/devices/device_manager.py

@@ -16,8 +16,8 @@
     UserData,
 )
 from roborock.devices.device import DeviceReadyCallback, RoborockDevice
-from roborock.exceptions import RoborockException
 from roborock.diagnostics import Diagnostics
+from roborock.exceptions import RoborockException
 from roborock.map.map_parser import MapParserConfig
 from roborock.mqtt.roborock_session import create_lazy_mqtt_session
 from roborock.mqtt.session import MqttSession