Traverse: Pytree traversal utility

Ops

flatten	Flatten an arbitrary python object into a tree definition and a collection of leaves.
unflatten	Repack a tree definition and list of leaves into the original python object.

Nodes

InternalObject	Special type indicating an unconstrained type.
LeafObject	Special type indicating an unconstrained type.
ScalarObject	Special type indicating an unconstrained type.
InternalNode	Node correponding to unpackable container.
LeafNode	Leaf node, typically corresponding to a tensor.
ScalarNode	Special type indicating an unconstrained type.