Add virtual nodes to the Monte Carlo Tree

[jingyuanlm]

Description

Motivation and Context

How Has This Been Tested?

• If you are adding a new feature, test on your own test scripts.

Screenshots of Test Results (if appropriate):

1. Your own tests:

Types of changes

• Fix bugs
• Add new feature
• Update documentation

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📚 Documentation preview 📚: https://RDAgent--1300.org.readthedocs.build/en/1300/

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[you-n-g]

Make it the class attribute

[you-n-g]

create a new get_parents function

[you-n-g]

I think this if else should be placed into the _get_u_uct function.

[you-n-g]

I think this can be simplified