Add additional test coverage for lazy imports

[brittanyrey]

We have a bunch of lazy imports tests in facebookincubator/cinder that we've carried for the PEP 690 implementation. I've identified a gap between the Cinder lazy imports test suite and the tests we added for PEP 810. I'd like to port some of those tests over to increase coverage.

Specific coverage areas to tackle:

• Dict operations with lazy values (copy, |, update, values/items)
• Attribute side effects (submodule imports don't overwrite parent attrs)
• Module/variable name collisions (submodule vs variable ordering)
• Deleted module reimport (sys.modules deletion and reimport)
• Circular import resolution (lazy imports breaking circular deadlocks)
• Custom __import__ via exec with lazy imports
• Dict mutation during module loading

Linked PRs

• gh-150565: Add additional tests for Lazy Imports #149739
• [3.15] gh-150565: Add additional tests for Lazy Imports (GH-149739) #158614

[StanFromIreland]

Triage: can this be closed as completed?