final_env_response pattern; updated docs/tests/example

[willccbb]

Description

Introduces proper support for rollouts to include final_env_response in state, which can be set in env_response, resulting in early termination mid-step.

We treat these as cosmetic/metadata, accessible by Rubric classes + for logging, but not included in trajectory (as token representations are never materialized).

Resolves #671 ; replaces #673

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Test improvement

Testing

• All existing tests pass when running uv run pytest locally.
• New tests have been added to cover the changes

Checklist

• My code follows the style guidelines of this project as outlined in AGENTS.md
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Additional Notes

---

Note

Implements a clean termination path for multi-turn rollouts when the environment produces a final message.

• Core changes: add state["final_env_response"] (initialized in Environment.init_state), new stop condition has_final_env_response, rollout loop skips extra model call when set, and _render_completion appends the final env message for scoring while keeping it out of the trajectory
• Wordle: on game completion, sets final_env_response and returns it; minor typing/casting cleanups
• Docs: refine MultiTurnEnv example, make ToolEnv sample tool async, and add a "Final Environment Responses" section describing the pattern and its effects
• Tests: add coverage for early stop and completion inclusion; mark env package tests as slow; minor warning-filter tweak in pyproject.toml

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