Adding PatchTST, renaming d_innner into d_ffn, and refactoring Autofomer

[WenjieDu]

What does this PR do?

1. add PatchTST as an imputation method;
2. rename d_innner into d_ffn;
3. refactor Autofomer;

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 8472120672

Details

• 162 of 172 (94.19%) changed or added relevant lines in 14 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 82.098%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pypots/nn/modules/transformer/layers.py	7	10	70.0%
pypots/imputation/patchtst/model.py	72	79	91.14%

Files with Coverage Reduction	New Missed Lines	%
pypots/cli/env.py	1	65.31%

Totals
Change from base Build 8449119065:	0.3%
Covered Lines:	5627
Relevant Lines:	6854

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💛 - Coveralls