A stale suspicion timer could declare a node dead even after it had been
refuted back to Alive via a higher incarnation number. check_suspicion_timeouts
now verifies the node is still Suspect before calling declare_dead, and
cancels the probe phase if the dead node was the current target.
Also fix the 3-node gossip loop in node_death_tombstones_entries to
deliver responses with the correct sender_id — previously all responses
were attributed to a single hardcoded sender, causing false suspicions
that triggered the protocol bug.
Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski
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