Update PremadeSampleDataset signature (#312)

Author: Sukh-P

pvnet/data/base_datamodule.py

@@ -4,6 +4,7 @@
 
 from lightning.pytorch import LightningDataModule
 from ocf_data_sampler.numpy_sample.collate import stack_np_samples_into_batch
+from ocf_data_sampler.sample.base import SampleBase
 from ocf_datapipes.batch import (
     NumpyBatch,
     TensorBatch,
@@ -22,9 +23,10 @@ class PremadeSamplesDataset(Dataset):
 
     Args:
         sample_dir: Path to the directory of pre-saved samples.
+        sample_class: sample class type to use for save/load/to_numpy
     """
 
-    def __init__(self, sample_dir: str, sample_class):
+    def __init__(self, sample_dir: str, sample_class: SampleBase):
         """Initialise PremadeSamplesDataset"""
         self.sample_paths = glob(f"{sample_dir}/*")
         self.sample_class = sample_class