Improve help for types that have choices

[multimeric]

For example, if you have a Pydantic model with an enum type, the flag will be displayed as:

  --skew SKEW           (type:DeskewDirection default:DeskewDirection.Y)

Similarly, if you use a Literal:

class Model(BaseModel):
    bar: Literal["x", "y"]

you get:

  --bar BAR             (type:typing.Literal['x', 'y'] required=True)

In all of these cases, we have a readily accessible list of options, and it would be much more user friendly to provide these in the help.

Compare this to argparse's choices, which are printed as:

usage: game.py [-h] {rock,paper,scissors}