Upgrade scikit learn to recent versions

[SuperBo]

Proposed changes

Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request. If it fixes a bug or resolves a feature request, be sure to link to that issue.

Scikit Learn changes theirs tree implementation through recent versions. This Pull Request is to add changes to adapt with latest SkLearn version.

First, I detect sklearn version then define Cython compile env to detect SKLearn version.

Types of changes

What types of changes does your code introduce to CausalML?

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Further comments

Nothing added.

[CLAassistant]

All committers have signed the CLA.

[jeongyoonlee]

Thanks for your contribution, @SuperBo. Your PR is similar and related to #686, submitted earlier. Once merged, it will remove the scikit-learn dependency and allow users to use whichever scikit-learn version they want.

I look forward to your next contribution.