[WIP] Integrate Liger CPO & SimPO

[Mecoli1219]

What does this PR do?

Integrating Liger-kernel's CPO and SimPO losses into cpo_trainer.

Related to #2495

TODO:

• Update Liger-kernel's aux-output to include chosen_rewards andrejected_rewards

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[Mecoli1219]

Wait for linkedin/Liger-Kernel#492