Add parallel tool execution with concurrency controls

[ryaneggz]

Summary

• refactor tool execution to support parallel batches with configurable concurrency, scheduler hooks, result streaming, and sequential fallback warnings
• extend ToolIntent metadata and update documentation to describe new options and return telemetry from executeTools
• add unit tests verifying concurrency limits, deterministic ordering, error aggregation, and onResult callback behaviour

Testing

• npm run build
• npx tsx --test --env-file=.env.test test/execute-tools.test.ts
• npm test (fails: missing OPENAI_API_KEY)

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https://chatgpt.com/codex/tasks/task_e_68e45e87caf4832881b70053680d71ce