• added unit-test in test-device-init:
  • initializes multiple clients all at once in different processes - this makes them happen simultaneously and failed
• ignore init messages after init
• stop init loop once done
• ignore init messages if we're still waiting for a device-header
  • i.e., before we get the device-header, we ignore already in-progress init sequences

and:

• improve exception handling in rspy.test
• add pyrealdds.device_server.publish_notification()
• improve docs for device initialization, to cover "atomic" initialization

Tracked on [LRS-797]