Align tests with features

[dkg]

I was experimenting with variants like:

cargo test --no-default-features --features ml-kem-512

and noticed that many permutations of features will cause the test suite to fail in different ways.

This series annotates the tests (including the doctests) with the appropriate features to ensure that they should normally pass.

The one scenario where they don't pass is if none of the ml-kem-512, ml-kem-768, or ml-kem-1024 features are enabled. That is, these two ways of running still fail:

cargo test --no-default-features
cargo test --no-default-features --features default-rng

I think that's probably OK. It would be nice if Cargo.toml could somehow be annotated explicitly that at least one of the ml-kem-* features must be enabled. I don't know how to do that, though.

Note that the first commit in this series actually tunes up one of the documentation examples so that it doesn't rely on the default-rng feature, before annotating it for reliance on ml-kem-512. If you think it really should depend on both ml-kem-512 and default-rng even though it uses a *_with_rng function elsewhere, please go ahead and adjust it in that way.

[dkg]

I looked at the errors in the clippy test, and they look like this:

error: item has both inner and outer attributes
   --> src/lib.rs:322:1
    |
322 | / /// Functionality for the ML-KEM-512 security parameter set, which is claimed to be in security category 1, see
323 | | /// table 2 & 3 on page 33 of spec.
324 | | #[cfg(feature = "ml-kem-512")]
325 | | pub mod ml_kem_512 {
...   |
338 | |     //!
339 | |     //! **--> See [`traits`] for the keygen, encapsulation, decapsulation, and serialization/deserialization functionality.**
    | |_____________________________________________________________________________________________________________________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mixed_attributes_style
note: the lint level is defined here
   --> src/lib.rs:2:27
    |
2   | #![deny(clippy::pedantic, warnings, missing_docs, unsafe_code)]
    |                           ^^^^^^^^
    = note: `#[deny(clippy::mixed_attributes_style)]` implied by `#[deny(warnings)]`

This series doesn't touch src/lib.rs at all, or add any inner attributes, for that matter. So i think the test failure is unrelated to the proposed changes here. Indeed, i think this might be a bug in clippy's mixed_attributes_style linter, which might be misidentifying //! …[ as an inner attribute (why else would it show lines 338 and 339 in the error message?)

[integritychain]

Thanks for your work here, I like it! I think I may know what's up with clippy and can fix.