Force Backends to implement Debug trait

[phated]

Problem

If backends don't derive the Debug trait, we can't use them as a generic in combination with deriving thiserror::Error. I encountered this in noir-lang/noir#1322 and added derive(Debug) to the aztec_backend, but we should enforce it via traits.

Proposed solution

Add + Debug to the backend trait.

Alternatives considered

No response

Additional context

No response

Submission Checklist

• Once I hit submit, I will assign this issue to the Project Board with the appropriate tags.