Make serde_bytes a mandatory dependency

[zeenix]

Given how much faster serde_bytes use makes (de)serialization of byte arrays, we should make it mandatory and advertise it more (e.g with examples in the crate docs).

Since turning an optional dependency into mandatory, breaks existing code, we can't just do it in non-major version updates.

[zeenix]

Since turning an optional dependency into mandatory, breaks existing code, we can't just do it in non-major version updates.

Actually it might be possible to do this by adding a dummy feature by the same name. We'll see when I get to implement this.

[zeenix]

Hmm.. thinking more about this, I don't think we should do this. Not everyone needs to (de)serialize byte sequences directly and it's not good to mandate another dep. However we should:

• Add a proxy cargo feature to zbus, so serde-bytes can be enabled in zvariant, when used through zbus (recommended).
• Advertise/document it more visibly.