Integrate emergency checkpointer into standalone_checkpointer for CPUs.

[RoshaniN]

1. When local checkpoints are available for restore, alter mesh setup as follows.

• Ignore the JAX coordinator provided by XPK and override the JAX coordinator to be the pod containing process_id 0.
• Persist the IP address of this pod using socket APIs to GCS.
• Let other processes retrieve the address of this coordinator, similar to TPUs.

2. Restore state and not state["items"] if emergency checkpoint manager is enabled.

3. Some changes in Jax/Orbax are needed to get this working end-to-end on CPUs. Other changes are addressed in this PR.

[xuefgu]

Can you please resolve the conflicts first? I see that the last update was from 2 weeks ago.