FREEDOM, added back the optimization loop code in learner_server.py

Ran experiment with pushcube env from maniskill. The learning seem to work.

Co-authored-by: Adil Zouitine <adilzouitinegm@gmail.com>

lerobot/common/logger.py

@@ -259,7 +259,7 @@ class Logger:
                 if k == custom_step_key:
                     continue
 
-                if self._wandb_custom_step_key is not None:
+                if self._wandb_custom_step_key is not None and custom_step_key is not None:
                     # NOTE: Log the metric with the custom step key.
                     value_custom_step_key = d[custom_step_key]
                     self._wandb.log({f"{mode}/{k}": v, self._wandb_custom_step_key: value_custom_step_key})