`impl SomeType` as a parameter on a mocked method does not compile

[nrxus]

Example: if a parameter to a mocked function is &impl serde::Serialize, faux will fail to compile.

The culprit is this line:

let input: (#(#arg_types),*) = unsafe { std::mem::transmute((#(#arg_idents),*)) };

This becomes:

 let input: (&impl serde::Serialize) = unsafe { std::mem::transmute((_x0)) };

There is an issue for using impl on a let binding but I am unsure how the transmute might work with that: rust-lang/rust#63065 🤷‍♂️

[nrxus]

The problem with the way the code is expanded is "fixed" in 500e9a9 but impl arguments or any generic argument still does not work. Tracked in #18