refactor(factory, pi0fast): Update processor function names and parameters

- Renamed make_pi0_processor to make_pi0fast_processor for clarity and consistency.
- Updated parameter names in the factory's make_processor function to use pretrained_model_name_or_path instead of source, enhancing readability and alignment with naming conventions.

src/lerobot/policies/factory.py

@@ -144,12 +144,12 @@ def make_processor(
         # TODO(azouitine): Handle this case.
         return (
             RobotProcessor.from_pretrained(
-                source=pretrained_path,
+                pretrained_model_name_or_path=pretrained_path,
                 config_filename=kwargs.get("preprocessor_config_filename", "robot_preprocessor.json"),
                 overrides=kwargs.get("preprocessor_overrides", {}),
             ),
             RobotProcessor.from_pretrained(
-                source=pretrained_path,
+                pretrained_model_name_or_path=pretrained_path,
                 config_filename=kwargs.get("postprocessor_config_filename", "robot_postprocessor.json"),
                 overrides=kwargs.get("postprocessor_overrides", {}),
             ),

src/lerobot/policies/pi0fast/processor_pi0fast.py

@@ -27,7 +27,7 @@ from lerobot.processor import (
 )
 
 
-def make_pi0_processor(
+def make_pi0fast_processor(
     config: PI0Config, dataset_stats: dict[str, dict[str, torch.Tensor]] | None = None
 ) -> tuple[RobotProcessor, RobotProcessor]:
     input_steps = [