Attempt to mark various generated code with #[automatically_derived]

[alex]

fixes #3989

[alex]

Haven't verified this is sufficient yet, just putting it up here for visibility.

[alex]

@davidhewitt on deeper review, I don't think this is going to work. My read of https://github.com/rust-lang/rust/pull/120185/files suggests that it only works on methods from impl blocks which are marked, it won't work on free-functions that #[pyfunction] generates.

[davidhewitt]

Ah, that's frustrating.

I think the best hope for debugging in that case is to trigger a cryptography CI run with one or more of the #[pyfunction]s with coverage issues replaced by its expanded form from cargo expand. Hopefully that will show us what's not covered so we can think how to improve this.