[WIP] Update SAC configuration and environment settings

- Reduced frame rate in `ManiskillEnvConfig` from 400 to 200.
- Enhanced `SACConfig` with new dataclasses for actor, learner, and network configurations.
- Improved input and output feature management in `SACConfig`.
- Refactored `actor_server` and `learner_server` to access configuration properties directly.
- Updated training pipeline to validate configurations and handle dataset repo IDs more robustly.

lerobot/configs/train.py

@@ -106,8 +106,9 @@ class TrainPipelineConfig(HubMixin):
             train_dir = f"{now:%Y-%m-%d}/{now:%H-%M-%S}_{self.job_name}"
             self.output_dir = Path("outputs/train") / train_dir
 
-        if isinstance(self.dataset.repo_id, list):
-            raise NotImplementedError("LeRobotMultiDataset is not currently implemented.")
+        if self.dataset is not None:
+            if isinstance(self.dataset.repo_id, list):
+                raise NotImplementedError("LeRobotMultiDataset is not currently implemented.")
 
         if not self.use_policy_training_preset and (self.optimizer is None or self.scheduler is None):
             raise ValueError("Optimizer and Scheduler must be set when the policy presets are not used.")