Restore NCCL INFO debug level, remove per-batch noise

TRACE was too verbose. INFO shows clean transport selection lines
(NET/IB, GPU Direct RDMA status) for both ranks via stderr redirect.
Per-batch logging removed; per-epoch summary kept with timing.

Co-Authored-By: Claude <noreply@anthropic.com>

dags/test-train-pytorch.py

@@ -44,7 +44,7 @@ def run_training_node_func(rank, world_size):
   os.dup2(sys.stdout.fileno(), sys.stderr.fileno())
 
   # CRITICAL: Set NCCL environment variables BEFORE importing torch
-  os.environ['NCCL_DEBUG'] = 'TRACE'
+  os.environ['NCCL_DEBUG'] = 'INFO'
   os.environ['NCCL_TIMEOUT'] = str(NCCL_TIMEOUT)
   os.environ['TORCH_NCCL_BLOCKING_WAIT'] = '1'
   os.environ['NCCL_IB_DISABLE'] = '0'  # Enable InfiniBand
@@ -285,7 +285,6 @@ def run_training_node_func(rank, world_size):
           optimizer.step()
 
           epoch_loss += loss.item()
-          print(f"[{rank}] Epoch {epoch+1}/{num_epochs} Batch {batch_idx+1}/{num_batches} | Loss: {loss.item():.6f}")
 
       avg_loss = epoch_loss / num_batches
       epoch_time = time.time() - epoch_start