feat: add mark_saved

rust/automerge/src/automerge.rs

@@ -698,6 +698,11 @@ impl Automerge {
         bytes
     }
 
+    /// Mark the document as saved
+    pub fn mark_saved(&mut self) {
+        self.saved = self.get_heads();
+    }
+
     /// Save the changes since the last call to [Self::save`]
     ///
     /// The output of this will not be a compressed document format, but a series of individual