Update HCMGNN dataset and code comments

[longlifeseelive]

Description

This PR updates the dataset implementation by switching to GMD4HCMGNN. It introduces an automatic download mechanism to improve user experience and refactors the codebase to fix deprecated/incorrect logic and standardize comments.

Checklist

• Changes are complete
• All changes have test coverage
• Code is well-documented
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
• Related issue is referred in this PR

Changes

• Dataset Migration: Replaced the previous dataset with GMD4HCMGNN.
• Auto-Download Feature: Added logic to automatically download and extract the dataset if it's not found locally.
• Code Refactoring: Fixed inappropriate logic/bugs discovered during testing.
• Documentation & Localization: Translated Chinese comments into English (or standardized them) and improved internal docstrings for better readability.