feat(pkg): add isSyncing method (#379)

pkg/rpc/methods.go

@@ -96,10 +96,7 @@ func (c *Client) WaitTillL2ExecutionEngineSynced(ctx context.Context) error {
 				return err
 			}
 
-			if progress.SyncProgress != nil ||
-				progress.CurrentBlockID == nil ||
-				progress.HighestBlockID == nil ||
-				progress.CurrentBlockID.Cmp(progress.HighestBlockID) < 0 {
+			if progress.isSyncing() {
 				log.Info("L2 execution engine is syncing", "progress", progress)
 				return errSyncing
 			}
@@ -281,6 +278,14 @@ type L2SyncProgress struct {
 	HighestBlockID *big.Int
 }
 
+// isSyncing returns true if the L2 execution engine is syncing with L1.
+func (p *L2SyncProgress) isSyncing() bool {
+	return p.SyncProgress != nil ||
+		p.CurrentBlockID == nil ||
+		p.HighestBlockID == nil ||
+		p.CurrentBlockID.Cmp(p.HighestBlockID) < 0
+}
+
 // L2ExecutionEngineSyncProgress fetches the sync progress of the given L2 execution engine.
 func (c *Client) L2ExecutionEngineSyncProgress(ctx context.Context) (*L2SyncProgress, error) {
 	ctxWithTimeout, cancel := ctxWithTimeoutOrDefault(ctx, defaultTimeout)