dsa: introduce `serde`

[sivizius]

This commits introduces the dependency serde to dsa. It is gated by two features: serde and serde_secrets. The first only derives Deserialize and Serialize for non-secret types like Signature. The latter additionally for SignatureKey, which should be used with caution, because it could allow accidentally leaking secrets.

[sivizius]

Draft, because serde_secrets should be implemented with serdect. Or any other "constant time" way.

[tarcieri]

Yeah, it would be good to use serdect, similar to how ecdsa does it, especially since you're doing secret key serialization (i.e. SigningKey)

[sivizius]

Yeah, it would be good to use serdect, similar to how ecdsa does it, especially since you're doing secret key serialization (i.e. SigningKey)

I am actually working on an commit/PR which introduces another crate common with common types that can be used across all other crates, initially with two types: Bytes and SecretBytes which would move the zeroisation, (de)serialisisation, etc. into these type, thus harmonise (de)serialisation, etc.

[tarcieri]

I'd prefer not to add superfluous crates. There shouldn't be that much duplication.

[tarcieri]

Closing as stale