feat: add PipeWire multi-channel audio driver (full-duplex N channel)

- PipeWireDriver.hpp/cpp: new AudioDriver implementation using pw_filter API
- Full-duplex I/O via pw_filter (capture + playback in one RT callback)
- Dynamic channel count support (tested: 1-8 channels, extensible beyond)
- Uses SPA_AUDIO_FORMAT_F32 for zero-copy-compatible float processing
- Channel position mapping: MONO, stereo, 5.1, 7.1, plus Aux for N>8
- Follows the same buffer management pattern as AlsaDriverImpl
- Channel routing: main/aux input/output mapping with mix ops
- CLI flag: --driver pipewire|alsa (default: alsa)
- AudioHost: conditional driver selection based on driverType_
- PiPedalModel: stores and passes driver type to AudioHost
- CMakeLists.txt: added PipeWireDriver source files

src/main.cpp

@@ -185,6 +185,7 @@ int main(int argc, char *argv[])
     bool testExtraDevice = false;
     std::string logLevel;
     std::string portOption;
+    std::string driverOption = "alsa";
 
     CommandLineParser parser;
     parser.AddOption("-h", &help);
@@ -193,6 +194,7 @@ int main(int argc, char *argv[])
     parser.AddOption("-log-level", &logLevel);
     parser.AddOption("-port", &portOption);
     parser.AddOption("-test-extra-device", &testExtraDevice); // advertise two different devices (for testing multi-device connect)
+    parser.AddOption("--driver", &driverOption);
 
     try
     {
@@ -226,6 +228,7 @@ int main(int argc, char *argv[])
                   << "   -systemd: Log to systemd journals instead of to the console.\n"
                   << "   -port: Port to listen on e.g. 80, or 0.0.0.0:80\n"
                   << "   -log-level: (debug|info|warning|error)\n"
+                  << "   --driver: Audio driver (alsa|pipewire, default: alsa)\n"
                   << "Example:\n"
                   << "    pipedald /etc/pipedal/config /etc/pipedal/react -port 80 \n"
                      "\n"
@@ -398,6 +401,7 @@ int main(int argc, char *argv[])
                 });
 
             model.Init(configuration);
+            model.SetDriverType(driverOption);
 
             // Get heavy IO out of the way before letting dependent (Jack/ALSA) services run.
             model.LoadLv2PluginInfo();