Refactor FeatureExpander Class for Improved Clarity and Functionality

[singhtanishq]

This pull request refactors the FeatureExpander class in the following ways:

• Modularizes noise addition to edges into the add_noise_to_edges method.
• Modularizes edge removal into the remove_specified_edges method.
• Modularizes node grouping by degree into the group_nodes_by_degree method.
• Ensures all functionalities and the overall workflow of the original code are preserved.

These changes enhance the readability and maintainability of the code without altering its core functionality.

• Adds support for grouped nodes by degree.
• Cleans up feature calculation methods.

Please review the changes and provide feedback.