ConstGenericPlaceholder

[oscartbeaumont]

I wonder if we make it positional instead of as string (Eg. usize vs &'static str). It would be nice because we can have const generics for numbers but not strings in the current release.

If that idea isn't possible we might just have to live with the fact that Rust isn't going to release the feature we need until after Specta v2 drops.