take out output dataloader

[xzrderek]

Note

Removes support for custom output data loaders and standardizes trace fetching via Fireworks.

• Drop output_data_loader from GithubActionRolloutProcessor and RemoteRolloutProcessor; always use default_fireworks_output_data_loader
• Update tests to monkeypatch/wrap the default loader to track rollout_ids; remove bespoke loaders; deprecate test_remote_langfuse
• Remote server: sanitize messages into OpenAI-compatible dicts (exclude None) and use that payload in completions
• Minor doc/example updates (TypeScript server README) and small assertions/cleanups in tests

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