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.