Handles discovery replies for traceroute measurements.
Initializes a TraceSession for a traceroute from the catching worker to the target.
Also instruct the catching Worker to send a Trace with TTL = 1.
Awaits Trace replies (i.e., ICMP Time Exceeded).
Updates the corresponding TraceSession, including the timeout, and follows
up with the next Trace task according to the session’s progress strategy: