fix: ensure S7 constructor matches class name to avoid identity check…

[Yunuuuu]

Fix partial: #6544

S7::new_class("CraftBox",
    properties = list(
        plot = ggplot2::class_ggplot
    )
)
#> Error: `ggplot2::ggplot` is not identical to the class with the same @package and @name properties

This commit ensures that the constructor has the same name as the S7 class, and it attaches the original class name to the object during construction.

[Yunuuuu]

[teunbrand]

I don't like changing the class names. They're used in error messages and it'll expose implementation details that are confusing to users.