Use #[serde(with = "serde_bytes")]

[robin-nitrokey]

Instead of using &serde_bytes::Bytes as the field type, we should use &[u8] with #[serde(with = "serde_bytes")] so that serde_bytes is only an implementation detail and not a public dependency.

Blocked by:

• Support serde(with = "…") serde-indexed#13