[client] usb audio: add microphone recording

Add a composite UAC2 microphone function with its own clock so
recording and playback can use independent sample rates.

Packetize asynchronous capture through usbredir, follow the host
capture clock, and preserve the newest frames across stalls.

Reconfigure active recording without another permission prompt and
fix lost PipeWire capture wakeups.

client/src/audio.c

@@ -2156,7 +2156,7 @@ static void realRecordStartLocked(const LG_AudioFormat * format)
   audio.audioDev->record.start(format, recordPushFrames);
 
   // if a volume level was stored, set it before we return
-  if (audio.record.volumeChannels)
+  if (audio.record.volumeChannels && audio.audioDev->record.volume)
     audio.audioDev->record.volume(
         audio.record.volumeChannels,
         audio.record.volume);
@@ -2201,7 +2201,8 @@ static void recordConfirm(bool yes, void * opaque)
 static void recordStart(const LG_AudioFormat * format)
 {
   LG_LOCK(audio.record.lock);
-  if (!audio.audioDev || audio.record.shuttingDown ||
+  if (!audio.audioDev || !audio.audioDev->record.start ||
+      audio.record.shuttingDown ||
       !audioFormatValid(format))
   {
     if (format && !audioFormatValid(format))
@@ -2271,6 +2272,29 @@ static void recordStart(const LG_AudioFormat * format)
   app_msgBoxClose(oldConfirm);
 }
 
+static void recordReconfigure(const LG_AudioFormat * format)
+{
+  LG_LOCK(audio.record.lock);
+  if (!audio.audioDev || !audio.audioDev->record.start ||
+      audio.record.shuttingDown || !audioFormatValid(format))
+  {
+    LG_UNLOCK(audio.record.lock);
+    return;
+  }
+
+  audio.record.lastFormat = *format;
+  if (audio.record.started &&
+      !audioFormatEqual(format, &audio.record.format))
+  {
+    realRecordStopLocked();
+    realRecordStartLocked(format);
+  }
+  else if (audio.record.confirmPending)
+    audio.record.confirmFormat = *format;
+
+  LG_UNLOCK(audio.record.lock);
+}
+
 static void realRecordStopLocked(void)
 {
   audio.audioDev->record.stop();
@@ -2522,9 +2546,12 @@ static void eventRecordStart(void * opaque, uint32_t generation,
     binding->ops->recordData;
   if (active)
   {
-    atomic_store_explicit(&audio.record.streamGeneration,
-        generation, memory_order_release);
-    recordStart(format);
+    const uint32_t previous = atomic_exchange_explicit(
+        &audio.record.streamGeneration, generation, memory_order_acq_rel);
+    if (previous == generation)
+      recordReconfigure(format);
+    else
+      recordStart(format);
   }
   LG_UNLOCK_SHARED(audio.activeLock);
 }