Fix math verify timeout

[mikasenghaas]

Description

math-verify uses handlers with signal.alarm to implement parsing and verification timeouts. These may cause race conditions in async contexts. This PR updates the MathRubric class to avoid this issue:

• Passes None as timeout to all math_verify function so that internal timeouts are not used
• Runs all synchronous blocking operations with asyncio.to_thread(...)
• Implements a global timeout using asyncio.wait_for(...)
  Adds basic tests to ensure that timeouts are enforced correctly.

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