Consistent hashing ring

Build a consistent-hashing ring used to assign keys to storage nodes. The ring has 2^16 = 65536 slots. Each physical node is placed at `vnodes` virtual positions computed deterministically as h(node_id, i) = (i * 2654435761 + sum(ord(c) for c in node_id) * 40503) % 65536 for i in 0..vnodes-1. A key hashes to position k(key) = (sum(ord(c) for c in key) * 2654435761) % 65536. A key is owned by the first node position at or clockwise after k(key) (wrapping around). Process operations: ["add", node_id], ["remove", node_id], and ["owner", key]. Return the list of owner results (the owning node_id, or empty string "" if the ring has no nodes), in order. If two virtual nodes land on the same slot, the one added earlier wins that slot.