Enhance Python AST extractor for Django support and improve route handling

- Added handling for assignment nodes in the AST to capture Django urlpatterns at the module level.
- Updated the expression statement handler to also process Django urlpatterns.
- Enhanced the decorated definition handler to back-fill route facts with the corresponding handler names.
- Improved dependency tracking by changing the target format in import statements.
- Modified the function handling to distinguish between methods and top-level functions.
- Updated tests to use a unified extraction function and removed redundant file handling code.
- Cleaned up unused helper tests and ensured consistent handling of class and function definitions.

Author: GertL