LeafSpec

The spec of a single leaf: TreeSpec(*).

:func:`~clika_runtime.pytree.tree_flatten` returns an instance of this class
when the tree is a leaf, so ``isinstance(spec, LeafSpec)`` tells a lone
value from a container.

>>> pytree.tree_structure(3)
TreeSpec(*)
>>> isinstance(pytree.tree_structure(3), pytree.LeafSpec)
True

__init__

__init__(self, *, none_is_leaf: 'bool' = True, namespace: 'str' = '') -> 'None'

Initialize self. See help(type(self)) for accurate signature.