Implement is_not_defaulted_loan functionality

[codebestia]

Description

This PR implement the is_not_defaulted_loan functionality. the functionality checks whether a loan is still active and not defaulted. This function builds on top of is_valid_loan and adds a time-based check to ensure that the loan has not passed its repayment deadline

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Configuration change

Checklist

Development Best Practices

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• New and existing tests pass locally with my changes

Testing

• Unit tests cover the new functionality
• Integration tests verify the changes work with other components

Related Issues

Fixes #27