No error when parsing unknown arguments after verb

You can try this with your CLI program (replace `program.exe verb` as appropriate):

`program.exe verb unknownarg`

Replace unknownarg with any random inputs as long as they don't start with `-` and `Parser.Default.ParseArguments` will return `ParserResult.WithParsed`.

It doesn't matter what the value of `ParserSettings.IgnoreUnknownArguments` is.

I don't know if this is a bug or just hasn't been implemented but this is a fundamental problem with the built-in validation of this library.

Does anyone have any solutions to catch unknown args?

Start by reproducing `program.exe verb unknownarg` through `Parser.Default.ParseArguments`, varying `ParserSettings.IgnoreUnknownArguments` as described. Trace the verb and positional-argument parsing path; the issue is done when an unknown argument is handled consistently with the intended validation behavior and the reported case is covered by a regression test.

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