I believe this will optimize execution inside AVM, right?

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.

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

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

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

@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