Add support for generics and impl Trait types

[foresterre]

• TODO:
  • Figure out limitations to this approach. Will it scale with async for example
  • Where should the __generated fn be placed? Is it good enough to put it in the module, or, especially for custom macro's, do we want the implementation to be stacked inside the #[maybe_my_custom_test] fn?

Can we replace the current binding based implementation completely? Or do we want or need to keep both?

#[parameterized(a = { 0 }, b = { 1 })]
fn numbers<T: Into<u8>>(input: T) {
    assert_eq!(0, input)
}

mod test {
    #[test]
    fn a() {
        fn __generated<T: Into<u8>>(input: T) {
            assert_eq!(0, input.into());
        }

        __generated(0); 
    }

    #[test]
    fn b() {
        fn __generated<T: Into<u8>>(input: T) {
            assert_eq!(0, input.into());
        }

        __generated(1);
    }
}

and

fn __generated(input: impl Into<u8>) {
            assert_eq!(0, input.into());
        }

        __generated(0);
}