🐛 Add support for an argument of type Optional[Tuple] and default value None

[Asthestarsfalll]

Support optional tuples like this:

from typing import Optional, Tuple
import typer

def main(arg: Optional[Tuple[int]] = None):
    pass

typer.run(main)

[svlandeg]

I relabeled this as a bug, as it feels like this is functionality that you'd expect to work, but currently doesn't on master. The fix seems correct to me, and I've slightly rewritten the unit test to be even more in line with the preceding test_optional().

Thanks for your contribution!

[tiangolo]

Great, thanks for your contribution @Asthestarsfalll! 🚀

And thanks for the help @svlandeg! 🙇 🍰