Quattro

- Restore TaskGroup copyright notice.
- TaskGroups now raise ExceptionGroups (using the PyPI backport when necessary) on child errors.
- Add support for Python 3.11, drop 3.8.
- TaskGroups no longer have a `name` and the `repr` is slightly different, to harmonize with the Python 3.11 standard library implementation.
- TaskGroups no longer swallow child exceptions when aborting, to harmonize with the Python 3.11 standard library implementation.
- Switch to CalVer.

- Add `py.typed` to enable typing information.
- Flesh out type annotations for TaskGroups.

- Add {meth}`quattro.current_effective_deadline`.

- Initial release, containing task groups and cancellation scopes.