Stop caching pytree structure in all cases. Caching was resulting in a bug when using `enable_flax=False` in conjunction with existing checkpoints that had been saved with a msgpack structure fle.
Stop caching pytree structure in all cases. Caching was resulting in a bug when using `enable_flax=False` in conjunction with existing checkpoints that had been saved with a msgpack structure fle.

PiperOrigin-RevId: 476962160

google/orbax