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?

まず、`Parser.Default.ParseArguments` を通じて `program.exe verb unknownarg` を再現し、説明どおりに `ParserSettings.IgnoreUnknownArguments` を変化させます。verb と位置引数のパース経路を追跡します。不明な引数が意図した検証動作と一貫して処理され、報告されたケースが回帰テストでカバーされた時点で issue は完了です。

索引モデルが issue の本文から書いたものです。