Migrate lints to use 2024 edition practice of unsafe_op_in_unsafe_fn

[davidhewitt]

Credit to @jonaspleyer for the work here in #4976, I accidentally closed that PR and now can't push to that branch. (Calling it main made it awkward for me to push to, sorry 😬)

I added an additional commit which should hopefully fix the MSRV build...

[davidhewitt]

Having started down this road, I am now considering resetting this for pyo3-ffi and explicitly marking #[allow(unsafe_op_in_unsafe_fn)] for that whole crate.

Justification: the contents of pyo3-ffi are deliberately written as a faithful translation of the CPython source code, and having the unsafe { } all over the place just adds to the translation burden without really improving the situation (i.e. we need to match the CPython implementations anyway).

@alex (as you commented on the original PR) - what do you think about partially backing this out?

For the main pyo3 crate I think warn(unsafe_op_in_unsafe_fn) is 100% justified.

[alex]

I don't feel strongly. Certainly it seems fine to me if we want to start with just doing the pyo3 crate, and then maybe we can consider pyo3-ffi later.

[jonaspleyer]

Some type of network error seems to have killed the windows cross-compilation workflow. 😐

[davidhewitt]

Yes, it downloads some build tools. We cache them but they keep getting evicted, will try #4995...

[mejrs]

Having started down this road, I am now considering resetting this for pyo3-ffi

A bit late but I agree, it's a bit silly for a crate that's all just unsafe.

[jonaspleyer]

Having started down this road, I am now considering resetting this for pyo3-ffi

A bit late but I agree, it's a bit silly for a crate that's all just unsafe.

I think it has been included in ed37c40. See https://github.com/PyO3/pyo3/blob/ea5adbf90413d524fe89ffe00c4ed6f219dafe09/pyo3-ffi/src/lib.rs#L337C6-L337C34.
In particular this does provides forward Compatibility for users already on edition 2024. They will not get swarmed with warnings relating to this lint which is nice. I think that it is a good choice to have it like this.