[Port HIL_SERL] Final fixes for the Reward Classifier (#598)

tests/policies/hilserl/classifier/test_modelling_classifier.py

@@ -1,7 +1,6 @@
 import torch
 
 from lerobot.common.policies.hilserl.classifier.modeling_classifier import (
-    Classifier,
     ClassifierConfig,
     ClassifierOutput,
 )
@@ -21,6 +20,8 @@ def test_classifier_output():
 
 @require_package("transformers")
 def test_binary_classifier_with_default_params():
+    from lerobot.common.policies.hilserl.classifier.modeling_classifier import Classifier
+
     config = ClassifierConfig()
     classifier = Classifier(config)
 
@@ -40,6 +41,8 @@ def test_binary_classifier_with_default_params():
 
 @require_package("transformers")
 def test_multiclass_classifier():
+    from lerobot.common.policies.hilserl.classifier.modeling_classifier import Classifier
+
     num_classes = 5
     config = ClassifierConfig(num_classes=num_classes)
     classifier = Classifier(config)
@@ -60,6 +63,8 @@ def test_multiclass_classifier():
 
 @require_package("transformers")
 def test_default_device():
+    from lerobot.common.policies.hilserl.classifier.modeling_classifier import Classifier
+
     config = ClassifierConfig()
     assert config.device == "cpu"
 
@@ -70,6 +75,8 @@ def test_default_device():
 
 @require_package("transformers")
 def test_explicit_device_setup():
+    from lerobot.common.policies.hilserl.classifier.modeling_classifier import Classifier
+
     config = ClassifierConfig(device="meta")
     assert config.device == "meta"