Use alternate RPC providers on error

[rupurt]

Given a blockchain adapter
When it receives errors from an RPC call
Then it should try the alternate RPC providers according to the configured strategy

The venue configuration DSL will need an additional option

config :slurp,
  blockchains: %{
    "ethereum-mainnet" => %{
      start_on_boot: false,
      name: "Ethereum Mainnet",
      adapter: Slurp.Adapters.Evm,
      network_id: 1,
      chain_id: 1,
      chain: "ETH",
      testnet: false,
      timeout: 5000,
      new_head_initial_history: 128,
      poll_interval_ms: 2_500,
      rpc: [
        "https://cloudflare-eth.com",
        # This can take N extra RPC providers
        "https://main-light.eth.linkpool.io"
      ],
      # Optionally add RPC strategy. Defaults to `nil`
      rpc_strategy: {Slurp.RpcStrategies.RoundRobinOnError, :next, [[count: 5, per: 1, unit: :minute]]}
    },
  }

[rupurt]

@AwaitFuture ^