Showing the accepted input type

Like [the blog post](https://swift.org/blog/argument-parser/) mentions:

> Because `highValue` is defined as an `Int`, only valid inputs are recognized, with no manual parsing or casting necessary on your part:

```
> random ZZZ
Error: The value 'ZZZ' is invalid for ''
Usage: random
```

Would it be possible to give an indication that an `Int` is expected rather than the invalid `String`?

No source file or test is named. Start by reproducing the invalid `ZZZ` input behavior from the issue and trace the argument-validation and error-formatting entry points; done means the diagnostic indicates that an `Int` is expected while preserving the shown usage output.

Written by the indexing model from the issue text.