* Implement Optional required, when creating a ModelField(required=True), make it persist
* Add test for nullable required
* Improve formatting of Undefined custom object
* Refactor field infer/creation with Undefined to make it idempotent
Needed for when _type_analysis is re-run in Generics
* Add PR changes
* Increment/update tests with code review
* Update/refactor Undefined implementation with code review
* Fix BoolUndefined as string type for mypy, not runtime
* Add docs about required Optional
* Add explicit tests for Any
* Apply code review requested changes
* move tests out of test_validators.py
Stephen Brown II