feat(alsa): duplex stream support - #1347
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Opens capture and playback from the same pcm_id and drives both from one worker thread. Links them via snd_pcm_link() where possible; virtual PCMs (default, pulse, asym) don't support that, so linking failure is tolerated and both handles are started and polled independently instead.
roderickvd
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This PR adds native duplex support for ALSA. It works well on my laptop, which isn't a whole lot of testing, but at least it's something.
Capture and playback open on the same
pcm_idand negotiate matching period sizes. Where the driver and hardware support it,snd_pcm_link()ties the two together so they also start/pause/stop/recover together. When they don't (e.g. anasymPCM spanning two cards), it proceeds unlinked instead of refusing the stream - they could be slaved to an external clock without cpal ever knowing.src/host/alsa/mod.rswas getting really large so as a separate commit that was split into submodules.