Changes to jax optimizers.py to facilitate serialization of optimizer state.
Changes to jax optimizers.py to facilitate serialization of optimizer state.

Co-authored-by: Matthew Johnson <e68678f07030b810d1440f7f1c1c423f5afe56fe@google.com>

tensorflow/probability,tensorflow/probability,google/jax,google/jax,google/jax,google/jax