Add Windows WASAPI backend

[iancharest]

Goal

Add native Windows playback and capture support using WASAPI.

Scope

• Device enumeration
• Output playback
• Input capture
• Ring-buffer-backed stream behavior matching macOS semantics
• Stream stats parity with macOS
• CI/wheel support for Windows x86_64 and, if feasible, arm64

Acceptance Criteria

• tachyaudio.list_devices() returns Windows audio devices
• examples/play_tone.py works on Windows
• examples/capture_level.py works on Windows
• Tests pass on supported Python versions

Notes

Keep Windows-specific behavior behind the backend protocol.