Nargo should cache CRS instead of leaving to backends

[phated]

Problem

Currently, backends are expected to implement caching, but aztec_backend puts artifacts into nargo-controlled directories. Nargo CLI should handle the caching of CRS files.

Proposed solution

Implement a backend trait such as noir-lang/acvm#231 and implement it in aztec_backend and then consume the new API in Nargo and handle caching (via filesystem, or whatever) inside Nargo CLI.

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.