#3510 Detect event-loop blocking in tests

Summary

• add BlockBuster to detect blocking calls from mcp and mcp_types
• exempt coverage internals, jsonschema lazy imports, and synchronous media conversion
• resolve Windows executables off the event loop

Tests

• ./scripts/test
• uv run --frozen ruff format --check .
• uv run --frozen ruff check .
• uv run --frozen pyright

AI Disclaimer

This PR was developed with the assistance of either Claude or Codex. I've reviewed and verified the changes.