Add Trackio rollout trace logging

[abidlabs]

Hi folks! This PR adds trace logging via Trackio, the free, local-first experiment tracking library from Hugging Face 🤗

This PR follows Tunix's existing rollout and trajectory logging patterns. Specifically, I did this:

• added optional Trackio trace settings to AlgorithmConfig
• added PPO/GRPO rollout prompt-completion logging as trackio.Trace records with step/reward/advantage metadata
• added agentic trajectory logging as trackio.Trace records with trajectory metadata
• documented Trackio rollout trace logging
• added tests with mocked Trackio

Here's what it looks like:

AI assistance was used to prepare this PR.

[lc5211]

Thanks for the PR! Can we make trackio as one backend of TrajectoryLogger to make the logging system more manageable? Thanks!

[abidlabs]

Thanks for the suggestion @lc5211. I updated this PR to make Trackio a backend of the existing trajectory logger instead of using a separate Trackio-specific logger. The Trackio backend now lives in tunix/utils/trajectory_logger.py, standard RL and agentic RL both dispatch traces through AsyncTrajectoryLogger

I also tested and confirmed with and end-to-end example that everything is logged correclty: