添加了SlotGAT

[zhuqiming1025]

Description

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• Changes are complete (i.e. I finished coding on this PR)
• 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
• If the PR is for a new model/paper, I've updated the example index here.

Changes

[CfromBU]

阻塞：提交了大量 TensorBoard event 文件到 openhgnn/output/GTN、openhgnn/output/RGCN、openhgnn/output/SlotGAT，这是运行产物，不能进 PR。

[CfromBU]

虽然 SlotGAT.py 有 @register_model('SlotGAT')，但 dataset 接入是 SlotGATDataLoader 特例，不是标准 @register_dataset/BaseDataset 风格。

[CfromBU]

SlotGAT_dataset.py 使用 dgl.DGLGraph(...) 旧接口，含乱码注释和大量原始文件解析逻辑。
没有 README。