sha2 `compress256` no longer public

[TomAFrench]

After #678, sha2::compress256 is no longer public with no obvious replacement. The fact that the function is still marked pub implies that this isn't an intentional change.

We use the compression function over at https://github.com/noir-lang/noir so it would be great to be able to continue using the implementation from this crate going forwards.

[TomAFrench]

Looks like these crates have quite a few items which are marked pub but are inaccessible. Is there any interest in turning on the unreachable_pub warning? (I'd be happy to set this up and adjust visibility to get it passing.)

[tarcieri]

@TomAFrench that sounds good to me, as does re-exporting them as it also seems like an oversight to me. They were deliberately exported by request.

[TomAFrench]

Cool, I'll make a PR.

[TomAFrench]

Turns out these are actually still exported through sha2::block_api::compress256 so I'm going to close this issue. I've left the PR open in case you want to maintain the top-level export.

[tarcieri]

It’d be good to add a CHANGELOG entry since it’s confusing they moved

[TomAFrench]

Looks like it's already there 😬 😅