Add pyproject.toml, replace deprecated sdist command

[onixlas]

Copy project metadata to pyproject.toml (PEP 621), replace deprecated python setup.py sdist with python -m build -s.

All Submissions Basics:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you checked all Issues to tie the PR to a specific one?

All Submissions Cores:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?
• Does your submission pass tests, including CircleCI, Travis CI, and AppVeyor?
• Does your submission have appropriate code coverage? The cutoff threshold is 95% by Coversall.

New Model Submissions:

• Have you created a .py in ~/pyod/models/?
• Have you created a _example.py in ~/examples/?
• Have you created a test_.py in ~/pyod/test/?
• Have you lint your code locally prior to submission?

[coveralls]

Pull Request Test Coverage Report for Build 12455408348

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 95.361%

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Totals
Change from base Build 12453182960:	0.0%
Covered Lines:	10361
Relevant Lines:	10865

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💛 - Coveralls

[onixlas]

Hi, @yzhao062 ,

I hope you're doing well! I wanted to check in on this pull request and #617 , both submitted about six months ago. I understand that maintaining a project takes time and effort, but I’d appreciate any updates on whether there’s anything I can do to help move it forward.

I was planning to contribute more small improvements in the future, but the lack of feedback on this PR makes me a bit hesitant. If there are specific reasons it hasn’t been merged or if it’s no longer relevant, I’d be happy to hear your thoughts.

Thanks for your time and for maintaining this library!