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/data_factory.py

@@ -1,5 +1,5 @@
 from data_provider.data_loader import Dataset_ETT_hour, Dataset_ETT_minute, Dataset_Custom, Dataset_M4, PSMSegLoader, \
-    MSLSegLoader, SMAPSegLoader, SMDSegLoader, SWATSegLoader, UEAloader
+    MSLSegLoader, SMAPSegLoader, SMDSegLoader, SWATSegLoader, UEAloader, Dataset_PEMS, Dataset_Solar
 from data_provider.uea import collate_fn
 from torch.utils.data import DataLoader
 
@@ -15,7 +15,9 @@ data_dict = {
     'SMAP': SMAPSegLoader,
     'SMD': SMDSegLoader,
     'SWAT': SWATSegLoader,
-    'UEA': UEAloader
+    'UEA': UEAloader,
+    'PEMS': Dataset_PEMS,
+    'Solar': Dataset_Solar,
 }