Improve runtests and CI pipeline

[ytdHuang]

Here are the summary changes for this PR, which I think is quite necessary to do before getting more and more people involved to contribute to this package.

1. Separate different testsets into individual files, which would be better for everyone to cooperate in the future
2. use SafeTestsets to make all testsets be really independent with each other (I found some small bugs in the original runtests, like one is using the variables in another testset)
3. Separate the CI pipeline into runtests and documentation
4. For both CIs, I changed the situations for triggering them, and also automatically skip for draft PR
5. For runtests CI, I add the os (MacOS and Windows)
6. For runtests CI, I add the keyword group: Core, to specify that we are testing core functionalities for our packages (this is just in case that we might have extensions in the future)

I'm making these changes based on my habits, of course it doesn't necessarily to do it in my way.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.74%. Comparing base (e19924e) to head (93687f8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #38   +/-   ##
=======================================
  Coverage   89.74%   89.74%           
=======================================
  Files          17       17           
  Lines        1619     1619           
=======================================
  Hits         1453     1453           
  Misses        166      166           

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