Zero-segment Workaround

[notlesh]

TITLE

Remove call to add_zero_zegment() in Mod builtin

Description

This PR works around an issue related to run_validity_checks() where the mul_mod builtin has an additional memory segment which causes the index verification to fail here.

This isn't meant to be a viable fix. I suspect that a proper fix would be to account for the additional segments in the index checks in run_validatity_checks() or similar.

However, the zero_segment functionality (introduced here) is unclear to me, so this is meant as a temporary workaround to help us progress in SNOS.

If anyone is able to explain the zero_segment functionality and how it relates to run_validity_checks(), I'll be happy to work on a better fix.

Checklist

• Linked to Github Issue
• Unit tests added
• Integration tests added.
• This change requires new documentation.
  • Documentation has been added/updated.
  • CHANGELOG has been updated.