bug fix: centralized v8 mutex

[eliasposen]

Description

Fixed JS runtime race condition by moving the V8 mutex to be held for the entire typecheck/execute process.

Related Issues

Fixes #
Related to #

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Performance improvement
• Code refactoring
• Test coverage improvement

Changes Made

• Centralized V8 mutex

Testing

• added test_concurrent_execute_stress which recreates this scenario

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Test Commands Run

cargo test
cargo clippy
cargo fmt --check

Breaking Changes

• This PR includes breaking changes
• Migration guide updated in CHANGELOG.md

Documentation

• Code comments added/updated
• README.md updated (if needed)
• CHANGELOG.md updated under "Unreleased"
• API documentation updated

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published

Screenshots/Videos

Additional Context