[Sorts] General refac/minor changes Sorts issue

This is a high level, general issue so we don't mix some tasks with some specific issues.

The main purpose of this issue is to gather small refactor tasks or small code changes non related to Sorts main functionality but to code split/refactor/tests etc., those kind of low-priority tasks.

I'll be frequently updating the list below with those low-priority/code refactor tasks that could arise over time.

• Typing module
• Constants module
• Make Sorts import packages like Integrates. One domain imports other domain by doing backend.X_domain.Y_function instead of X_domain.Y_function despite both are at the same level.
• Improve tests
• Define a data-model
• Add new models to test
• Add SOPS to Sorts
• Add model info in execution