Return bytes instead of str

Closes https://github.com/datpy/merkle-tree-stream/issues/2.

merkle_tree_stream/node.py

@@ -23,7 +23,7 @@ class MerkleTreeNode:
     parent: int
     size: int
     data: bytes
-    hash: Optional[str] = attr.Factory(str)
+    hash: Optional[bytes] = attr.Factory(bytes)
 
     def __attrs_post_init__(self) -> Any:
         """Initialise the parent index."""

merkle_tree_stream/tree.py

@@ -7,8 +7,6 @@ from flat_tree import FlatTreeAccessor
 
 from merkle_tree_stream.node import MerkleTreeNode
 
-Hash = str
-
 EMPTY_DATA = b''
 EMPTY_HASH = None
 
@@ -26,8 +24,8 @@ class MerkleTreeIterator:
     :param roots: The tree roots
     """
 
-    leaf: Callable[[MerkleTreeNode], Hash]
-    parent: Callable[[MerkleTreeNode, MerkleTreeNode], Hash]
+    leaf: Callable[[MerkleTreeNode], bytes]
+    parent: Callable[[MerkleTreeNode, MerkleTreeNode], bytes]
     roots: List[MerkleTreeNode] = attr.Factory(list)
 
     _position: int = 0