Add UniTS

[WenjieDu]

1. Model description

UniTS should be included in PyPOTS, and could start from the imputation task.

@inproceedings{gao2024units,
author = {Gao, Shanghua and Koker, Teddy and Queen, Owen and Hartvigsen, Thomas and Tsiligkaridis, Theodoros and Zitnik, Marinka},
title = {{UniTS}: a unified multi-task time series model},
year = {2024},
isbn = {9798331314385},
publisher = {Curran Associates Inc.},
address = {Red Hook, NY, USA},
booktitle = {Proceedings of the 38th International Conference on Neural Information Processing Systems},
articleno = {4463},
numpages = {43},
location = {Vancouver, BC, Canada},
series = {NIPS '24}
}

2. Check open-source status

• The model implementation is publicly available

3. Provide useful information for the implementation

https://github.com/mims-harvard/UniTS

[github-actions]

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