Implement Tach to define module boundaries

[emdoyle]

📥 Pull Request

📘 Description
This PR introduces Tach to maintain clean module boundaries. It is added as an optional dev dependency and as a CI check in GitHub Actions.

🎯 Goal
Particularly for new contributors, it is helpful to have an automatic check to validate that new changes do not violate the intended architecture of the project. Tach also serves as documentation of the logical flow of the project through tach.yml and tach show

🔍 Additional Context
https://docs.gauge.sh

If changes are made which introduce new cross-module dependencies, they will cause tach check to fail and point out the offending imports. If they represent an intentional design change, they can be acknowledged with tach sync.

🧪 Testing
Running tach check passes with this configuration.

[areibman]

Thanks @emdoyle !!