Add hash property with setter and getter

jupyter_ydoc/ybasedoc.py

@@ -114,6 +114,26 @@ def dirty(self, value: bool) -> None:
         """
         self._ystate["dirty"] = value
 
+    @property
+    def hash(self) -> Optional[str]:
+        """
+        Returns whether the document hash as computed by contents manager.
+
+        :return: The document hash.
+        :rtype: Optional[str]
+        """
+        return self._ystate.get("hash")
+
+    @hash.setter
+    def hash(self, value: str) -> None:
+        """
+        Sets the document hash.
+
+        :param value: The document hash.
+        :type value: str
+        """
+        self._ystate["hash"] = value
+
     @property
     def path(self) -> Optional[str]:
         """