Feature request: Arbitrary pointer-sized data in attributes

[nikvoid]

It may be useful to store arbitrary pointer-sized data in Shape. Currently the only attribute type supported is arbitrary text, and if you want, for example, associate some const value with field, you cannot do it properly.

const ID: usize = 42;

#[derive(Facet)
struct Struct {
    #[facet(const(id = ID))] // how should we call this attribute?
    x: u32,
}

// Add this variant to attribute enums
*Attribute::Const(&str, usize) // or use GenericPtr to allow wide pointers?