refactor(processors): share policy pipeline builders (#4016)

* refactor(processors): share policy pipeline builders

* Apply suggestions from code review

Co-authored-by: Martino Russi <77496684+nepyope@users.noreply.github.com>
Signed-off-by: Steven Palma <imstevenpmwork@ieee.org>

* fix(processor): solve style after commit suggestions

---------

Signed-off-by: Steven Palma <imstevenpmwork@ieee.org>
Co-authored-by: Martino Russi <77496684+nepyope@users.noreply.github.com>

src/lerobot/policies/pi05/processor_pi05.py

@@ -24,26 +24,17 @@ import torch
 from lerobot.configs import PipelineFeatureType, PolicyFeature
 from lerobot.processor import (
     AbsoluteActionsProcessorStep,
-    AddBatchDimensionProcessorStep,
-    DeviceProcessorStep,
-    NormalizerProcessorStep,
     PolicyAction,
     PolicyProcessorPipeline,
     ProcessorStep,
     ProcessorStepRegistry,
     RelativeActionsProcessorStep,
-    RenameObservationsProcessorStep,
     TokenizerProcessorStep,
-    UnnormalizerProcessorStep,
-    policy_action_to_transition,
-    transition_to_policy_action,
+    make_default_policy_processor_steps,
+    make_policy_processor_pipelines,
 )
 from lerobot.types import EnvTransition, TransitionKey
-from lerobot.utils.constants import (
-    OBS_STATE,
-    POLICY_POSTPROCESSOR_DEFAULT_NAME,
-    POLICY_PREPROCESSOR_DEFAULT_NAME,
-)
+from lerobot.utils.constants import OBS_STATE
 
 from .configuration_pi05 import PI05Config
 
@@ -135,18 +126,16 @@ def make_pi05_pre_post_processors(
         action_names=getattr(config, "action_feature_names", None),
     )
 
+    steps = make_default_policy_processor_steps(config, dataset_stats)
+
     # OpenPI order: raw → relative → normalize → model → unnormalize → absolute
     input_steps: list[ProcessorStep] = [
-        RenameObservationsProcessorStep(rename_map={}),  # To mimic the same processor as pretrained one
-        AddBatchDimensionProcessorStep(),
+        steps.rename_observations,  # To mimic the same processor as pretrained one
+        steps.add_batch_dim,
         relative_step,
         # NOTE: NormalizerProcessorStep MUST come before Pi05PrepareStateTokenizerProcessorStep
         # because the tokenizer step expects normalized state in [-1, 1] range for discretization
-        NormalizerProcessorStep(
-            features={**config.input_features, **config.output_features},
-            norm_map=config.normalization_mapping,
-            stats=dataset_stats,
-        ),
+        steps.normalize,
         Pi05PrepareStateTokenizerProcessorStep(max_state_dim=config.max_state_dim),
         TokenizerProcessorStep(
             tokenizer_name="google/paligemma-3b-pt-224",
@@ -154,26 +143,13 @@ def make_pi05_pre_post_processors(
             padding_side="right",
             padding="max_length",
         ),
-        DeviceProcessorStep(device=config.device),
+        steps.to_device,
     ]
 
     output_steps: list[ProcessorStep] = [
-        UnnormalizerProcessorStep(
-            features=config.output_features, norm_map=config.normalization_mapping, stats=dataset_stats
-        ),
+        steps.unnormalize,
         AbsoluteActionsProcessorStep(enabled=config.use_relative_actions, relative_step=relative_step),
-        DeviceProcessorStep(device="cpu"),
+        steps.to_cpu,
     ]
 
-    return (
-        PolicyProcessorPipeline[dict[str, Any], dict[str, Any]](
-            steps=input_steps,
-            name=POLICY_PREPROCESSOR_DEFAULT_NAME,
-        ),
-        PolicyProcessorPipeline[PolicyAction, PolicyAction](
-            steps=output_steps,
-            name=POLICY_POSTPROCESSOR_DEFAULT_NAME,
-            to_transition=policy_action_to_transition,
-            to_output=transition_to_policy_action,
-        ),
-    )
+    return make_policy_processor_pipelines(input_steps=input_steps, output_steps=output_steps)