change Now() to use UnixNano() instead of Nanosecond(), which just returns the...

change Now() to use UnixNano() instead of Nanosecond(), which just returns the Nanosecond offset of the given second which is not what we want
rtdt-manager.go: Implement process of getting twin EntityID based on realnet EntityID in event handler to apply event from realnet to twin
topology.go: Implement function to get a node by its UUID
Rename gosdn_slim.clab.yaml to realnet-clab.yaml
venv.go: getTypedValue() returns gnmi.TypedValue with the right type for the value passed in