One agent per node

Keeps an agent on each node of a three-node cluster. The type is declared with pinned=True, so each reference names the node with at= instead of letting the hash ring choose: each node reaches its own agent by its NodeId, the first node reaches all of them by the Members of its table, and also by the host:port address each node announces. The program adds a fourth node and shows that no agent moves; gracefully stops the second node and shows that its agent becomes unavailable, with no other node taking it over; and starts a new process at the same address, where the same reference answers again and the agent starts over from the initial state.

Needs local TCP ports 7441 to 7444 to be free.

cd examples/10-agent-per-node
uv run main.py