windows: add LHDC V5/aptX sink and low-latency audio path

[Loukious]

Summary

Adds a Windows WinUSB A2DP sink demo with SBC, LHDC V5, and optional aptX Classic/aptX HD decoding, together with the PortAudio changes needed for stable low-latency playback at high sample rates.

Highlights

• LHDC V5: 44.1/48/96/192 kHz, 16/24-bit stereo
• aptX Classic + aptX HD: 44.1/48 kHz stereo
• aptX endpoints are advertised only when an external openaptx0.dll decoder backend is available; no aptX decoder code/binary is bundled
• fixes Android aptX Classic media handling (no RTP header when SCMS-T is not enabled)
• decodes aptX/aptX HD one codec block at a time
• handles the observed LHDC V5 192 kHz transport layout with two [tag, sequence] subpacket prefixes per 20 ms A2DP payload
• aptX keeps its 40/48 ms PCM target/high-water limiter
• LHDC does not discard decoded PCM for latency control; testing showed queue trimming can cause audible hitches, especially around packet-burst boundaries
• PortAudio staging scales with sample rate (128 @ 48 kHz, 256 @ 96 kHz, 512 @ 192 kHz) to preserve a similar callback period
• Windows WASAPI shared-mode auto-convert fallback for rates rejected by the active Windows mix format; no exclusive-mode device takeover
• monotonic PortAudio producer/consumer counters prevent stale staging buffers from growing latency indefinitely

Validation

Tested on Windows 11 with an Intel Bluetooth controller and an Android 16 Xiaomi onyx source:

• SBC playback
• aptX Classic playback and repeated aptX <-> aptX HD switching
• LHDC V5 playback at 44.1, 48, 96 and 192 kHz
• 44.1 kHz capture replay: 5,628 LHDC frames decoded, 0 bad frames
• 192 kHz capture: 6,574 A2DP packets / 26,296 LHDC frames; after stripping the two transport subpacket prefixes, decoder replay completed with 26,296 good frames and 0 bad frames
• sustained 192 kHz playback is clean with the parser fix and without destructive LHDC PCM trimming

The external aptX backend is intentionally not included because libopenaptx is GPLv3; the sink omits aptX endpoints when the DLL is unavailable.