feat(pipeline): Enhance configuration filename handling and state file naming

- Introduced support for custom configuration filenames in the `save_pretrained` method, allowing users to specify a filename instead of the default.
- Improved state file naming to include step indices, preventing conflicts when multiple processors of the same type are saved.
- Added automatic detection for configuration files when loading from a directory, with error handling for multiple files.
- Updated tests to validate new features, including custom filenames and automatic config detection.

tests/processor/test_rename_processor.py

@@ -225,7 +225,7 @@ def test_save_and_load_pretrained():
         pipeline.save_pretrained(tmp_dir)
 
         # Check files were created
-        config_path = Path(tmp_dir) / "processor.json"
+        config_path = Path(tmp_dir) / "testrenameprocessor.json"  # Based on name="TestRenameProcessor"
         assert config_path.exists()
 
         # No state files should be created for RenameProcessor
@@ -283,7 +283,7 @@ def test_registry_based_save_load():
         # Verify config uses registry name
         import json
 
-        with open(Path(tmp_dir) / "processor.json") as f:
+        with open(Path(tmp_dir) / "robotprocessor.json") as f:  # Default name is "RobotProcessor"
             config = json.load(f)
 
         assert "registry_name" in config["steps"][0]