Refactoring file and directory handling

[guiparpinelli]

1. Pathlib Integration: The use of os module is replaced with Python's more modern pathlib module across various tools. This shift enhances readability and consistency in handling file paths.

2. Field Validation Enhancements:

   • A new field validator, check_directory_traversal, is implemented to prevent directory traversal attacks. It ensures the provided paths are within allowed directories.
   • The start_directory fields in both BuildDirectoryTree and PrintAllFilesInDirectory classes now use Path instead of str, ensuring better path handling.

3. Refactoring File Extensions Handling:

   • File extensions are now handled using a set (set[str]) instead of a list (list[str] | None). This change simplifies the logic for including file types in the output.

4. Improved Directory Traversal:

   • BuildDirectoryTree and PrintAllFilesInDirectory classes have been refactored to use recursive functions for directory traversal, enhancing their efficiency and readability.

5. Testing Adjustments:

   • Tests have been updated to reflect the changes in the implementation, particularly the use of pathlib and the new field validations.
   • A new test file, test_utils.py, is added to specifically test the check_directory_traversal function.