Fix QueueSubscribeSync and backoff errors (#146)

Core NATS subscriptions were incorrectly using `SubscribeSync` instead
of `QueueSubscribeSync` and both core and JetStream subscriptions were
waiting for the backoff period (default 5 seconds) for all iterations of
the worker loop, not just error conditions. This PR fixes both issues.

---------

Signed-off-by: John Schaeffer <jschaeffer@equinix.com>

events/nats_subscribe.go

@@ -14,7 +14,7 @@ func (c *NATSConnection) coreSubscribe(ctx context.Context, subject string) (<-c
 		"nats.subject", subject,
 	)
 
-	sub, err := c.conn.SubscribeSync(subject)
+	sub, err := c.conn.QueueSubscribeSync(subject, NATSConsumerDurableName(c.cfg.QueueGroup, subject))
 	if err != nil {
 		return nil, err
 	}
@@ -24,10 +24,12 @@ func (c *NATSConnection) coreSubscribe(ctx context.Context, subject string) (<-c
 	go func() {
 		for {
 			if err := c.nextMessage(ctx, sub, msgCh); err != nil {
-				if !errors.Is(err, context.DeadlineExceeded) {
-					logger.Errorw("error fetching messages", "error", err)
+				if errors.Is(err, context.DeadlineExceeded) {
+					continue
 				}
 
+				logger.Errorw("error fetching messages", "error", err)
+
 				select {
 				case <-ctx.Done():
 				case <-time.After(c.cfg.SubscriberFetchBackoff):
@@ -70,10 +72,12 @@ func (c *NATSConnection) jsSubscribe(ctx context.Context, subject string) (<-cha
 	go func() {
 		for {
 			if err := c.fetchMessages(ctx, sub, msgCh); err != nil {
-				if !errors.Is(err, context.DeadlineExceeded) {
-					logger.Errorw("error fetching messages", "error", err)
+				if errors.Is(err, context.DeadlineExceeded) {
+					continue
 				}
 
+				logger.Errorw("error fetching messages", "error", err)
+
 				select {
 				case <-ctx.Done():
 				case <-time.After(c.cfg.SubscriberFetchBackoff):