feat: remove unnecessary usage of slices

[TomAFrench]

Description

Problem*

Resolves

Summary*

These calls are hiding an unnecessary conversion from arrays to slices and back to arrays. Instead we can now just move the array into the bignum.

This drops number of opcodes for the below program by 10% from 636 to 573

unconstrained fn main(a: Fq, b: Fq) -> pub Fq {
    a.__add(b)
}

Additional Context

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[kashbrti]

LGTM