Hybrid-pool-executor

- Add synchronized function support on `AsyncWorker`
- Add code coverage and PyPI badges in `README.md`
- Fix license info in `pyproject.toml`

- Refactor building wheel pipeline
- Update `README.rst`

- Refactor project structure
- Refactor `ModuleSpec`
- Split worker and manager into separated files
- Add `mypy` for lint test
- Fix `ThreadManager.stop` not working

Initial release of hybrid-pool-executor.

- Functional on Linux.
- Setup initial project CI pipelines.