Add new generative model: TIGER

[lw-xundong]

Pull Request / 拉取请求

What does this PR do? / 这个PR做了什么？

This PR implements the TIGER framework and provides a complete runnable example.

Type of Change / 变更类型

• 🐛 Bug fix / Bug修复
• ✨ New model/feature / 新模型/功能
• 📝 Documentation / 文档
• 🔧 Maintenance / 维护

Related Issues / 相关Issues

Fixes #(issue number) / 修复 #(issue编号)

How to Test / 如何测试

# cd examples/generative 
    python  run_tiger_amazon_books.py \
    --base_model /t5-small \
    --output_dir ./ckp \
    --per_device_batch_size 256 \
    --learning_rate 5e-4 \
    --epochs 200 \
    --temperature 1.0

Checklist / 检查清单

• Code follows project style (ran python config/format_code.py) / 代码遵循项目风格（运行了格式化脚本）
• Added tests for new functionality / 为新功能添加了测试
• Updated documentation if needed / 如需要已更新文档
• All tests pass locally / 所有测试在本地通过

Additional Notes / 附加说明

Any other information for reviewers / 给审查者的其他信息

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 12.03320% with 212 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.96%. Comparing base (01bd90b) to head (ebd65f7).
⚠️ Report is 66 commits behind head on main.

Files with missing lines	Patch %	Lines
torch_rechub/utils/data.py	15.93%	153 Missing ⚠️
torch_rechub/models/generative/tiger.py	0.00%	58 Missing ⚠️
torch_rechub/models/generative/__init__.py	0.00%	1 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #173      +/-   ##
==========================================
+ Coverage   36.88%   38.96%   +2.07%     
==========================================
  Files          60       67       +7     
  Lines        4042     4643     +601     
==========================================
+ Hits         1491     1809     +318     
- Misses       2551     2834     +283     

Flag	Coverage Δ
unittests	38.96% <12.03%> (+2.07%)	⬆️

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