A DNS seed was dialled as one host:port, which reaches whichever address
the resolver lists first; two of testnet-seed.bitcoinsv.io's four nodes
accepted a connection and never answered, so cloak-cli's first testnet
and mainnet starts were refused although the seeds' nodes were up.

- Peer entries resolve to every address they hold (PeerAddresses), all
  dialled in parallel; the error names each address, its seed and why.
- The start goes on at the first peer that answers; the rest finish in
  the background, and one that connects after shutdown is closed.
- NetworkParams.dnsSeeds: the node's own seeds per network, plus
  GorillaPool's testnet nodes.
- Header sync asks peers in order of their handshake height, so a node
  stuck far behind is not the one asked.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>