turn decodeRelTimestamp into milliseconds

op-node/rollup/derive/span_batch.go

@@ -76,7 +76,7 @@ func (bp *spanBatchPrefix) decodeRelTimestamp(r *bytes.Reader) error {
  if err != nil {
  return fmt.Errorf("failed to read rel timestamp: %w", err)
  }
- bp.relTimestamp = timeint.FromUint64SecToSec(relTimestamp) // is relTimestamp in seconds or milliseconds?
+ bp.relTimestamp = timeint.FromUint64MilliToMilli(relTimestamp)
  return nil
 }