fix: update internal references in test imports

[iontodd]

This pull request fixes internal references in test imports, allowing external contributors to run the test files without encountering import errors. Updated imports now follow the patterns observed in other test files in the same directory.

Changes:

• Replaced internal-only imports with public equivalents in test files.
• Updated references to align with project conventions.
• Ensured that tests run successfully after the changes.

[iontodd]

The smallest possible change that will achieve this goal is to modify the imports from:
from google3.third_party.chronicle.cli import mock_test_utility to
import mock_test_utility

I'm open to this too, I just tried to align the references to similar files.