[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/main.c

@@ -1838,6 +1838,8 @@ int spiceThread(void * arg)
 #if ENABLE_USB_AUDIO
     if (usbRedir && !lgUsbRedir_process(usbRedir))
       DEBUG_WARN("Failed to process USB audio redirection");
+    if (usbAudio)
+      processTimeout = lgaUsb_recording(usbAudio) ? 1 : 10;
 #endif
 
     if ((status = purespice_process(processTimeout)) != PS_STATUS_RUN)