sim-lib/refactor: pass report logger into results method

We're going to need to start the report logger in its own task in the
commit that follows (so that we can log every minute). This preparatory
commit refactors creations of a PaymentResultLogger so that we can
easily spin up its run task in our existing join set.

sim-lib/src/lib.rs

@@ -549,7 +549,10 @@ impl Simulation {
             listener.clone(),
         ));
 
+        let result_logger = Arc::new(Mutex::new(PaymentResultLogger::new()));
+
         tasks.spawn(consume_simulation_results(
+            result_logger,
             results_receiver,
             listener,
             self.print_batch_size,
@@ -874,21 +877,25 @@ async fn produce_random_events<N: NetworkGenerator, A: PaymentGenerator + Displa
 }
 
 async fn consume_simulation_results(
+    logger: Arc<Mutex<PaymentResultLogger>>,
     receiver: Receiver<(Payment, PaymentResult)>,
     listener: Listener,
     print_batch_size: u32,
     no_results: bool,
 ) {
     log::debug!("Simulation results consumer started.");
 
-    if let Err(e) = write_payment_results(receiver, listener, print_batch_size, no_results).await {
+    if let Err(e) =
+        write_payment_results(logger, receiver, listener, print_batch_size, no_results).await
+    {
         log::error!("Error while reporting payment results: {:?}.", e);
     }
 
     log::debug!("Simulation results consumer exiting.");
 }
 
 async fn write_payment_results(
+    logger: Arc<Mutex<PaymentResultLogger>>,
     mut receiver: Receiver<(Payment, PaymentResult)>,
     listener: Listener,
     print_batch_size: u32,
@@ -906,8 +913,7 @@ async fn write_payment_results(
         None
     };
 
-    let mut result_logger = PaymentResultLogger::new();
-    let mut counter = 0;
+    let mut counter = 1;
     loop {
         tokio::select! {
             biased;
@@ -918,7 +924,7 @@ async fn write_payment_results(
             payment_report = receiver.recv() => {
                 match payment_report {
                     Some((details, result)) => {
-                        result_logger.report_result(&details, &result);
+                        logger.lock().await.report_result(&details, &result);
                         log::trace!("Resolved dispatched payment: {} with: {}.", details, result);
 
                         if let Some(ref mut w) = writer {