Make `#[derive(Copy)]` enough for both `Clone` and `Copy`

HKalbasi:

It is not just saving 7 letters, it can also improve the codegen for Clone:

The Clone derive already does that, so there is no argument here (there is some order required between the derives, I don't remember which should be above and which below, but if they're on the same line it always works).

HKalbasi:

And if it gets done over an edition, ... and it would no longer need complex compiler features.

Not true, since old editions must still be supported by the compiler.