feat: add PEMS and Solar dataset support

- Add Dataset_PEMS and Dataset_Solar classes for PEMS and Solar datasets
- Update data_factory.py to include new dataset mappings
- Fix M4 dataset handling with proper numpy array dtype
- Add PEMS-specific loss function (L1Loss) and inverse transform support
- Update validation logic for PEMS dataset with inverse scaling
- Fix M4 data loader insample mask calculation bug

Changes support new traffic and solar energy datasets while maintaining
backward compatibility with existing datasets.

data_provider/m4.py

@@ -129,10 +129,11 @@ class M4Meta:
     }  # from interpretable.gin
 
 
-def load_m4_info() -> pd.DataFrame:
+def load_m4_info(info_file_path: str) -> pd.DataFrame:
     """
     Load M4Info file.
 
+    :param info_file_path: Path to M4-info.csv file
     :return: Pandas DataFrame of M4Info.
     """
-    return pd.read_csv(INFO_FILE_PATH)
+    return pd.read_csv(info_file_path)