[segmentation.data.typing] Define sample data as a TypedDict

src/mednet/libs/segmentation/data/typing.py

 import typing
+from typing import TypedDict
 
 import torch
 from mednet.libs.common.data.typing import RawDataLoader
 
-Sample: typing.TypeAlias = tuple[
-    typing.Mapping[str, torch.Tensor], typing.Mapping[str, typing.Any]
-]
+
+class SegmentationData(TypedDict):
+    """Type for segmentation data."""
+
+    image: torch.Tensor
+    target: torch.Tensor
+    mask: torch.Tensor
+
+
+Sample: typing.TypeAlias = tuple[SegmentationData, typing.Mapping[str, typing.Any]]
 
 
 class SegmentationRawDataLoader(RawDataLoader):