support worker pool

[repl-samuel]

Description

Allow pctx session/mcp server to run multiple deno runtime by adding worker pool support. Each demo is run is its own v8 engine. see #71

Related Issues

Every call to execute() acquires this mutex and holds it for the entire duration — type checking + code execution. This is a single process-wide queue, so all concurrent /execute_typescript requests run strictly sequentially.

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

Testing

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