writer: Fix hash entries not being sorted

Keys were being sorted correctly but not the hash entries themselves...

This is required to avoid generating invalid documents as the official
BYML library performs binary searches.

byml/byml.py

@@ -317,7 +317,8 @@ def _write_nonvalue_node(self, stream: typing.BinaryIO, data, node_to_offset_map
         elif isinstance(data, dict):
             stream.write(self._u8(NodeType.HASH))
             stream.write(self._u24(len(data)))
-            for (key, value) in data.items():
+            for key in sorted(data.keys()):
+                value = data[key]
                 stream.write(self._u24(self._hash_key_table[key]))
                 node_type = self._to_byml_type(value)
                 stream.write(self._u8(node_type))