Refactor skeleton.to_json to serialize skeleton object without jsonpickle

sleap/skeleton.py

@@ -987,7 +987,7 @@ def to_json(self, node_to_idx: Optional[Dict[Node, int]] = None) -> str:
         """Convert the :class:`Skeleton` to a JSON representation.
 
         Args:
-            node_to_idx: optional dict which maps :class:`Node`sto index
+            node_to_idx: optional dict which maps :class:`Nodes`to index
                 in some list. This is used when saving
                 :class:`Labels`where we want to serialize the
                 :class:`Nodes` outside the :class:`Skeleton` object.
@@ -999,6 +999,7 @@ def to_json(self, node_to_idx: Optional[Dict[Node, int]] = None) -> str:
         Returns:
             A string containing the JSON representation of the skeleton.
         """
+        # TODO: Replace jsonpickle with a custom encoder from sleap-io.
         jsonpickle.set_encoder_options("simplejson", sort_keys=True, indent=4)
         if node_to_idx is not None:
             indexed_node_graph = nx.relabel_nodes(