Update 3: Backup RPC connection, on by default, used only when the main one fails

Lemniscate reads the chain and sends its housekeeping transactions through the official Robinhood Chain public RPC. We added a second, independent backup connection that is used only when the public RPC fails: every call still goes to the public RPC first, and the backup answers only the calls the public RPC just refused or could not reach. When the public RPC answers again, traffic goes straight back to it. Free RPC providers limit how many blocks one log query may cover, so the indexer asks the backup in small slices and still keeps up. Nothing changes for users except fewer stalls when the main provider has a bad moment.