refactor(anta): Change TestStatus to be an Enum for coding clarity

[gmuloc]

Description

In #740 we end up doing getargs(TestStatus) on a Literal type which feels very awkward. This PR defines a proper type for TestStatus based on built-in Python Enum (can be made better in Python 3.11 with StrEnum)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have run pre-commit for code linting and typing (pre-commit run)
• [x] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes (tox -e testenv)