Target-local accounting was spread across the managed driver: the event
counter increments were inline in publish_client_events, the authoritative
packets_sent was copied from the client at fifteen separate call sites, and
ManagedTargetOutcome was constructed twice from the same six fields.
TargetCounters::observe now owns the per-event accounting,
TargetRuntime::sync_packets_sent/record_packets_sent own the authoritative
sent count, and TargetRuntime::outcome owns outcome construction, replacing
the free target_outcome function and the inline copy in finish_target. No
counter is touched outside TargetRuntime any more.
The replies_received semantics are unchanged and now documented on both the
private counter and the public outcome field: on-time unique echo replies
only, with late unique replies counted by late. observe matches ClientEvent
exhaustively, so a new event variant must be classified deliberately.