feat(audio): merge native ALSA playback devices into the exclusive selector

[mikelexp]

Hi! This adds native ALSA playback-device enumeration on Linux and merges it with the existing GStreamer device list, so SONE can show real hardware PCM outputs even when PipeWire/WirePlumber does not expose them.

I added this because I wanted to use a FiiO Q1 MK2 as a direct ALSA device outside the PipeWire graph. With that setup, I can select it in Exclusive mode and get bit-perfect playback without PipeWire’s resampling or mixing path affecting the signal chain.

The implementation uses AI assistance, since I don’t code in Rust myself, but I tested it locally and it behaves correctly for my setup (ArchLinux/CachyOS). I know you’ll review the code carefully anyway, so I’m happy to defer to your judgment on anything I may have missed.

A few details on the behavior:

• It keeps the existing GStreamer-discovered devices for compatibility.
• It adds native ALSA playback PCMs, including devices that PipeWire hides.
• It preserves manual override support.
• It deduplicates and sorts the merged selector list.

Also, congratulations on SONE. I really love your software. It’s easily the best Tidal experience I’ve found on Linux.