Add SCINet modules and implement it as an imputation model

[WenjieDu]

What does this PR do?

1. fixing Add SCINet #405;

Before submitting

• This PR is made to fix a typo or improve the docs (you can dismiss the other checks if this is the case).
• Was this discussed/approved via a GitHub issue? Please add a link to it if that's the case.
• I have commented my code, particularly in hard-to-understand areas.
• I have written necessary tests and already run them locally.

[coveralls]

Pull Request Test Coverage Report for Build 9045213233

Details

• 298 of 324 (91.98%) changed or added relevant lines in 8 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.3%) to 82.745%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pypots/imputation/scinet/model.py	70	73	95.89%
pypots/nn/modules/scinet/layers.py	98	107	91.59%
pypots/nn/modules/scinet/backbone.py	93	107	86.92%

Files with Coverage Reduction	New Missed Lines	%
pypots/nn/modules/etsformer/layers.py	2	96.6%
pypots/nn/modules/timesnet/layers.py	3	95.45%

Totals
Change from base Build 9019991548:	0.3%
Covered Lines:	8488
Relevant Lines:	10258

---

💛 - Coveralls