implementation of md6 in pure rust

[truthixify]

implementation of md6 in pure rust.

[newpavlov]

We can not merge this implementation in such state.

Please, do not disable the Clippy lints, follow the trait API defined in the digest crate, keep the crate no_std-capable (i.e. your code should not have any Vecs), add a CI workflow config for this crate (you can use the md5 file for reference), add the crate to the workspace by modifying the root Cargo.toml file, and remove the md6/.gitignore file.

Our trait APIs are a bit complex (and not documented that well), so I recommend taking a look at other crates in this repository first.

[truthixify]

@newpavlov
I don't know why this is failing: sha2 / riscv64-zknh (pull_request)

[newpavlov]

The CI failure is fixed in #637, so you need to rebase to master.

[newpavlov]

Thank you! I have some surface-level comments for now. I will take a closer look at the algorithm implementation later.

[newpavlov]

Could you also add this crate to the algorithms table in the root README?

[newpavlov]

Also please add a CI job for this crate. You can use the md5 config for reference.

[truthixify]

Hello sir @newpavlov.

I've added all the changes sir.