Move `__init__.py` utility functions to a `utils.py` module.

[pvk-developer]

Problem Description

The __init__.py file currently contains utility functions that are not directly related to package initialization. To improve code organization and maintain a clean separation of concepts, these utility functions should be moved to a dedicated utils.py module.

Expected behavior

Everywhere that we are importing from copulas import <utility function> should be from copulas.utils import <utility function> instead.

Additional context

• Verify that this change does not break any existing functionality.
• Consider adding any missing documentation for these utility functions while moving them.
• Use functools to create the decorators if the utility function is meant to be a wrapper.