Change ! decay from () to ! to keep up with Rust 2024

[xunilrj]

Take the following rust program as an example:

fn main() {
    let a = None;
    println!("{:?}", std::any::type_name_of_val(&a));
    a = Some([todo!()]);
}

Rust prints "core::option::Option<[(); 1]>" on edition 2021, and "core::option::Option<[!; 1]>" on edition 2024.
This happens because they decide to no longer decay ! to (), see rust-lang/rust#123748

When we were implementing ! we decided to follow Rust, and we now need to decide if we follow edition 2024 or not. I vote to follow it in the future, so we keep differences to Rust only where we think makes a difference.