Feat: Add native Windows pip installation support with automated CI/CD

[visheshrwl]

Tried to resolve #804

feat: Add Windows pip installation support

• Add setup.py with CMake extension building and dependency auto-cloning
• Add pyproject.toml for modern Python packaging
• Add GitHub Actions CI/CD for automated wheel building
• Add WINDOWS_INSTALL.md guide and test_installation.py validator
• Transform complex manual Windows setup to simple 'pip install open-spiel'
• Fix CMake configuration for proper pyspiel.pyd placement
• Update README.md with Windows installation documentation

Enables native Windows pip installation, eliminating 20+ manual setup steps

[lanctot]

Wow, this is amazing, thank you!

We're a bit back-logged at the moment, so apologies upfront: it will take a bit of time for us to look into this, but it's something I was hoping we'd have for a long time!

[visheshrwl]

Thanks, glad to hear it! I know some tasks are failing at the moment, I mainly wanted to get a working draft out to unblock review and gather early feedback. I’ll keep iterating until it’s stable.

[lanctot]

Hi @visheshrwl just checking in.

I see a few instances of the tests passing. Does it mean you got it working?

A few changes have been made to these files since, I believe. And also there will be another one soon: #1418

Just curious in what state this is in and if you're still planning to work on it?

[visheshrwl]

Hi @lanctot ! Yes, I've got it working!

The PR is now complete and all tests are passing.

I'm monitoring the latest CI run to ensure everything stays green, then this should be good to merge. Happy to rebase on top of #1418 or any other changes as needed!