gh-118761: Add helper to ensure that lazy imports are actually lazy (#132614)

gh-118761: Add helper to ensure that lazy imports are actually lazy (#132614)

This ensures that if we jump through some hoops to make sure something is imported
lazily, we don't regress on importing it.

I recently already accidentally made typing import warnings and annotationlib eagerly.

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>