Implement *_{add,sub}_{signed,unsigned} methods.

[nlordell]

They were stabilized in Rust 1.66.

[NCGThompson]

Is there any reason (e.g. licensing incompatibility) to not just copy + paste the integer implementation macros from the core library? That seems to be the best option considering the goal is a common interface with the native integers. All of theses functions are derived from intrinsics already implemented.

[nlordell]

Is there any reason (e.g. licensing incompatibility) to not just copy + paste the integer implementation macros from the core library?

Would you copy the whole integer implementation macros? That's a nice idea and will experiment and see if it "just works" without modifications.

[NCGThompson]

see if it "just works" without modifications.

It won't completely. At least not while strictly using stable features. I don't think we will lose much my deleting the unstable stuff though. I'll get to it.