[recipe] [WIP] feat: TPPO [passed continuous running] [accuracy unverified]

[HanlinDu]

Co-author: [email protected]
Co-author: [email protected]

What does this PR do?

TPPO (Truncated PPO): An algorithm optimization for on-policy partial rollout on PPO. TPPO truncates long rollouts same as partial rollout, yet uses Extended GAE when calculating advantages. See https://arxiv.org/abs/2506.15050 for more details.
This PR applies TPPO on veRL from SEED implementation.

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