Allow CRS (Common Reference String) to be pre-downloaded and pointed to through setting

[kobyhallx]

Problem

As a user of the backend (package in case of Nargo CLI)
I would like to be able to point the backend to a directory where CRS data already exists
so that I can pre-download CRS data upfront to support caching and no network access scenario.

Proposed solution

Enable env variable setting to support reading CRS data from file

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.

[phated]

I believe this conflicts with noir-lang/noir#1302

[kobyhallx]

Won't do since acvm-backend-barretenberg will be decomissioned.