Improve Path Handling for Structure Commands

[httpdss]

Overview

This PR improves the handling of file paths within the generate and list commands of the struct_module.

Changes

• Introduced consistent path resolution for contribs directory using os.path.dirname and os.path.realpath.
• Simplified and clarified logic for determining file_path in generate.py.
• Enhanced logic in list.py to aggregate structures from multiple directories (structures_path and contribs).
• Ensured error handling and path existence checks are more robust and better logged.

Justification

• Resolving paths centrally reduces redundancy and the risk of bugs.
• Aggregating structures from multiple sources improves functionality and user experience.

Impact

• Commands generate and list now handle paths more reliably.
• Users benefit from more informative error messages and a broader set of structure files in the listing command.