PortAudio consumer: new ASIO multi-channel audio output with video-scheduled dispatch

[gmeisel01]

Adds a new PortAudio consumer providing ASIO multi-channel audio output, targeted at professional live event and LED wall deployments requiring more than 2 channels of audio output.

Architecture
Uses a lock-free FIFO ring buffer to bridge CasparCG's push model with PortAudio's pull callback model. Audio packets are video-scheduled (same approach as the OAL consumer fix) and written to the FIFO by a high-priority dispatch thread. The PortAudio callback reads from the FIFO on demand.

ASIO-only
Enumerates only ASIO devices with fuzzy name matching (space-insensitive). Requires ASIO drivers to be installed (hardware ASIO, ASIO4ALL, or FlexASIO). Logs a clear error with installation guidance if no ASIO device is found.

Auto-tuning latency compensation
Enabled by default. Measures timing error after each dispatch and adjusts compensation every 10 seconds (200+ samples, 75% correction factor). Correctly handles the systematic offset introduced by ASIO hardware buffer latency, which varies by device and buffer size.

Configuration (casparcg.config)

• device-name — ASIO device name (fuzzy matched, uses default if omitted)
• output-channels — number of output channels (default 2)
• buffer-size-frames — ASIO buffer size in frames (default 128)
• latency-compensation-ms — initial latency compensation (default 40ms, auto-tuned at runtime)
• fifo-ms — FIFO buffer size in milliseconds (default 50ms)
• auto-tune-latency — enable/disable auto-tuning (default true)