chore: add pytest-sugar to dev dependencies for improved DX

[ojaswa072]

This PR enhances the developer experience (DX) by introducing pytest-sugar and pytest for testing.

Changes Made:

• Refined requirements.txt: Created a three-tier dependency structure (Core, Optional, Development).
• Maintained Integrity: The core Advisory Engine remains strictly standard-library only with zero external dependencies.
• Updated Documentation: Added a clear installation guide in the README for new contributors.

✅ Verification:

• Ran pip install -r requirements.txt successfully.
• Verified pytest execution now shows the progress bar and "sugar" styling.
• Confirmed the core engine still runs using only the Python standard library.