Add Windows-only Build and Test workflow for Python 3.14

[devtrack]

Motivation

• Provide a dedicated CI workflow to build and test on Windows x64 with Python 3.14 to isolate Windows-specific issues.
• Allow manual workflow_dispatch runs for targeted debugging of the Windows + Python 3.14 configuration.
• Ensure the Windows job uses a fixed environment (windows-latest, x64, dotnet 8.0.x, Python 3.14) separate from the main matrix.

Description

• Add .github/workflows/windows-build-test-3.14.yml which defines a build-test job that runs on windows-latest.
• Configure .NET via actions/setup-dotnet@v5 (dotnet-version: '8.0.x') and Python 3.14 via astral-sh/setup-uv@v7 with architecture: x64 and activate-environment: true.
• Synchronize the virtual environment with uv sync --managed-python and expose pyvenv.cfg via cat .venv/pyvenv.cfg.
• Run embedding tests with dotnet test for net472 and net8.0, run Python tests with pytest --runtime coreclr and pytest --runtime netfx, and run dotnet test on src/python_tests_runner/; the Mono embedding tests set MONO_THREADS_SUSPEND: preemptive.

Testing

• No automated tests were executed for this change because it only adds a GitHub Actions workflow file.

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Codex Task

[Copilot]

Pull request overview

This PR adds a dedicated GitHub Actions workflow to build and test the project on Windows with Python 3.14, providing a mechanism for isolated testing and debugging of Windows-specific issues with the latest Python version.

Changes:

• Added a new workflow file that can be manually triggered via workflow_dispatch
• Configured Windows-latest runner with .NET 8.0.x and Python 3.14 (x64)
• Implemented comprehensive test suite including embedding tests for both .NET Framework and .NET Core, plus Python tests for CoreCLR and NetFX runtimes

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