Add tests for Math fallback behavior

[huhaha120]

Summary

• add tests that exercise parser fallback implementations when native Math hyperbolic/logarithm/numeric helpers are unavailable
• verify Math globals are restored after each fallback test
• keep the change tests-only; no source, threshold, or config changes

Validation

• npm test -> 482 passing
• npm run coverage -> lines 95.72%, functions 95.77%

Disclosure

This PR was prepared with AI assistance and human-reviewed before submission.