[deps] fix: make wandb optional dependency

verl/utils/tracking.py

@@ -15,7 +15,6 @@
 A unified tracking interface that supports logging data to different backend
 """
 
-import wandb
 
 from typing import List, Union
 
@@ -32,6 +31,7 @@ def __init__(self, project_name, experiment_name, default_backend: Union[str, Li
         self.logger = {}
 
         if 'tracking' in default_backend:
+            import wandb
             wandb.init(project=project_name, name=experiment_name, config=config)
             self.logger['tracking'] = wandb