fix: constrain ops only in constrained context

[olehmisar]

Description

Problem*

Resolves #91

Summary*

Constrain ops via evaluate_quadratic_expression only in constrained context.

Additional Context

@TomAFrench shouldvalidate_gt::<_, MOD_BITS>(divisor, remainder); from fn udiv_mod also be inside if !std::runtime::is_unconstrained()?

PR Checklist*

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

[olehmisar]

I believe this will optimize execution inside AVM, right?

[TomAFrench]

shouldvalidate_gt::<_, MOD_BITS>(divisor, remainder); from fn udiv_mod also be inside if !std::runtime::is_unconstrained()?

Yep, anything that checks the result is correct is unnecessary in the unconstrained context.

[olehmisar]

@TomAFrench review please. Review very carefully as IDK what i am doing

[TomAFrench]

We can do the same stuff in add and sub as well.

if std::runtime::is_unconstrained() {
  _sub(lhs, rhs)
} else {
  //existing code
}

[olehmisar]

@TomAFrench i added is_unconstrained checks in from_field, neg, add and sub. I believe tests for neg, add and sub in unconstrained context are required due to how they are implemented