Remove frost module

[conradoplg]

In frost-core we currently have

• crate: non-FROST types for signing and verifying
• crate::frost: FROST types
• crate::frost::{keys, round1, round2}: the rest

However ciphersuite crates have

• crate: non-FROST types for signing and verifying, and FROST types
• crate::{keys, round1, round2}: the rest

Change frost-core to follow the ciphersuite crates, merging crate::frost into crate:: and removing crate::frost and move child modules up accordingly.

This is a significant (though simple) refactoring so we should do this after all open PRs are merged

[hdevalence]

Would this be just moving code around, or changing what's exposed in the public API?

We're working on a FROST implementation here penumbra-zone/decaf377-rdsa#18 and would be happy to track any refactors there, just wondering if we should expect code we're currently using to disappear.

[conradoplg]

Would this be just moving code around, or changing what's exposed in the public API?

We're working on a FROST implementation here penumbra-zone/decaf377-rdsa#18 and would be happy to track any refactors there, just wondering if we should expect code we're currently using to disappear.

Just moving things around, basically users of frost-core would need to change imports from e.g. use frost_core::frost::SigningKey to use frost-core::SigningKey. It wouldn't affect ciphersuite crates, just frost-core.