Add comments to single.just and nested.just to explain why we are using the eip712sign within the repo

[zchn]

Description

A clear and concise description of the features you're adding in this pull request.

Tests

Please describe any tests you've added. If you've added no tests, or left important behavior untested, please explain why not.

Additional context

Add any other context about the problem you're solving.

Metadata

• Fixes #[Link to Issue]