Refactor: Improve type hinting in CoreUtilsMixin

[pyob-bot]

Summary of Changes

This PR improves type safety within src/pyob/core_utils.py by adding explicit type annotations to local variables and method signatures.

• Added explicit str type annotations to input_str variables in _win32_input and the Unix-based input method.
• Added a -> None return type hint to the restore_workspace method.

Technical Impact

• Code Quality: Enhances static analysis and IDE autocompletion support.
• Maintainability: Improves code readability and ensures consistency with modern Python type-hinting standards.
• Safety: Reduces the risk of type-related bugs by making variable expectations explicit.