Add Windows miniaudio backend support

[iancharest]

Summary

• Add Windows native backend support through vendored miniaudio using WASAPI.
• Share the miniaudio stream implementation across Linux and Windows through a small native lock/sleep portability layer.
• Add UTF-8/WASAPI device ID conversion so Windows device enumeration IDs can be reused for explicit stream selection.
• Link the Windows extension against the required system libraries.
• Add Windows test and wheel CI jobs, plus README/changelog/classifier updates.

Validation

• PYTHONPATH=src python -m unittest discover -s tests
• python -m compileall -q src tests examples
• python -m pip install . was attempted on Windows but blocked by missing local Microsoft C++ Build Tools: Microsoft Visual C++ 14.0 or greater is required.

Notes

This follows the previous Linux development path by reusing vendored miniaudio rather than adding another platform-specific audio dependency.