Improvements to math rubric

[mikasenghaas]

Description

Fixes to MathRubric:

• Run in thread pool with configurable number of workers for higher performance
• Warning logs on exceptions and timeouts
• Re-raise CancelledError so that timeouts don't show print warnings twice
• Suppress wrong math_verify logs (Timeout is disabled as parsing_timeout is None or <= 0, you must provide the logic for timeout interuption yourself to prevent code getting stuck.)

Also, use MathRubric in gsm8k for testing.

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

Run MathRubric parse/verify in a thread pool with proper timeout/logging, use it in gsm8k, and bump gsm8k to verifiers>=0.1.8.

• Rubrics (verifiers/rubrics/math_rubric.py):
  • Run parse/verify via ThreadPoolExecutor (configurable max_workers) with run_in_executor helper.
  • Enforce timeouts using asyncio.wait_for; re-raise CancelledError; add warning logs on failures/timeouts; suppress math_verify logs.
  • Clean up executor in __del__.
• Environment (environments/gsm8k/gsm8k.py):
  • Replace custom parser/rubric with vf.MathRubric; pass rubric.parser to SingleTurnEnv.
• Tests (tests/test_math_rubric.py):
  • Set max_workers=1 in timeout test.
• Packaging (environments/gsm8k/pyproject.toml):
  • Bump version to 0.1.3; require verifiers>=0.1.8.

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