Function start_rpc_servers 

pub fn start_rpc_servers(
    rpc_configuration: &RpcConfiguration,
    registry: Option<&Registry>,
    tokio_handle: &Handle,
    rpc_api: RpcModule<()>,
    rpc_runtime: Runtime,
    rpc_id_provider: Option<Box<dyn SubscriptionIdProvider>>,
) -> Result<Server, Error>

Starts RPC servers.