Sleep when no logs (#110)

## tl;dr

- Addresses PR feedback and has the indexer sleep for 1 second when no logs are received. 

## Potential improvements

- Start with a smaller sleep time and use exponential backoff

pkg/indexer/blockchain/rpcLogStreamer.go

@@ -18,6 +18,7 @@ const (
 	// Setting to 0 since we are talking about L2s with low reorg risk
 	LAG_FROM_HIGHEST_BLOCK = 0
 	ERROR_SLEEP_TIME       = 100 * time.Millisecond
+	NO_LOGS_SLEEP_TIME     = 1 * time.Second
 )
 
 // The builder that allows you to configure contract events to listen for
@@ -32,9 +33,16 @@ func NewRpcLogStreamBuilder(rpcUrl string, logger *zap.Logger) *RpcLogStreamBuil
 	return &RpcLogStreamBuilder{rpcUrl: rpcUrl, logger: logger}
 }
 
-func (c *RpcLogStreamBuilder) ListenForContractEvent(fromBlock int, contractAddress common.Address, topics []common.Hash) <-chan types.Log {
+func (c *RpcLogStreamBuilder) ListenForContractEvent(
+	fromBlock int,
+	contractAddress common.Address,
+	topics []common.Hash,
+) <-chan types.Log {
 	eventChannel := make(chan types.Log, 100)
-	c.contractConfigs = append(c.contractConfigs, contractConfig{fromBlock, contractAddress, topics, eventChannel})
+	c.contractConfigs = append(
+		c.contractConfigs,
+		contractConfig{fromBlock, contractAddress, topics, eventChannel},
+	)
 	return eventChannel
 }
 
@@ -68,7 +76,11 @@ type RpcLogStreamer struct {
 	logger   *zap.Logger
 }
 
-func NewRpcLogStreamer(client ChainClient, logger *zap.Logger, watchers []contractConfig) *RpcLogStreamer {
+func NewRpcLogStreamer(
+	client ChainClient,
+	logger *zap.Logger,
+	watchers []contractConfig,
+) *RpcLogStreamer {
 	return &RpcLogStreamer{
 		client:   client,
 		watchers: watchers,
@@ -97,12 +109,19 @@ func (r *RpcLogStreamer) watchContract(watcher contractConfig) {
 		default:
 			logs, nextBlock, err := r.getNextPage(watcher, fromBlock)
 			if err != nil {
-				logger.Error("Error getting next page", zap.Int("fromBlock", fromBlock), zap.Error(err))
+				logger.Error(
+					"Error getting next page",
+					zap.Int("fromBlock", fromBlock),
+					zap.Error(err),
+				)
 				time.Sleep(ERROR_SLEEP_TIME)
 				continue
 			}
 
 			logger.Info("Got logs", zap.Int("numLogs", len(logs)), zap.Int("fromBlock", fromBlock))
+			if len(logs) == 0 {
+				time.Sleep(NO_LOGS_SLEEP_TIME)
+			}
 			for _, log := range logs {
 				watcher.channel <- log
 			}
@@ -113,7 +132,10 @@ func (r *RpcLogStreamer) watchContract(watcher contractConfig) {
 	}
 }
 
-func (r *RpcLogStreamer) getNextPage(config contractConfig, fromBlock int) (logs []types.Log, nextBlock *int, err error) {
+func (r *RpcLogStreamer) getNextPage(
+	config contractConfig,
+	fromBlock int,
+) (logs []types.Log, nextBlock *int, err error) {
 	highestBlock, err := r.client.BlockNumber(r.ctx)
 	if err != nil {
 		return nil, nil, err
@@ -144,7 +166,11 @@ func (r *RpcLogStreamer) getNextPage(config contractConfig, fromBlock int) (logs
 	return logs, &nextBlockNumber, nil
 }
 
-func buildFilterQuery(contractConfig contractConfig, fromBlock int64, toBlock int64) ethereum.FilterQuery {
+func buildFilterQuery(
+	contractConfig contractConfig,
+	fromBlock int64,
+	toBlock int64,
+) ethereum.FilterQuery {
 	addresses := []common.Address{contractConfig.contractAddress}
 	topics := [][]common.Hash{}
 	for _, topic := range contractConfig.topics {