Fix experimental audio, add denoise, auto volume.Prep migration (#38874)

Uses the previously merged denoising crate (and fixes a bug in it that
snug in during refactoring) to add denoising to the microphone input. 

Adds automatic volume control for microphone and output.

Prepares for migrating to 16kHz SR mono:
The experimental audio path now picks the samplerate and channel count depending on a setting. It can handle incoming streams with both the current (future legacy) and new samplerate & channel count. These are url-encoded into the livekit track name

Release Notes:

- N/A

crates/denoise/src/engine.rs

@@ -138,13 +138,13 @@ impl Engine {
 
         const SPECTRUM_INPUT: &str = "input_2";
         const MEMORY_INPUT: &str = "input_3";
-        let memory_input =
+        let spectrum =
             Tensor::from_slice::<_, f32>(&self.in_magnitude, (1, 1, FFT_OUT_SIZE), &Device::Cpu)
                 .expect("the in magnitude has enough elements to fill the Tensor");
 
         let inputs = HashMap::from([
-            (MEMORY_INPUT.to_string(), memory_input),
-            (SPECTRUM_INPUT.to_string(), self.spectral_memory.clone()),
+            (SPECTRUM_INPUT.to_string(), spectrum),
+            (MEMORY_INPUT.to_string(), self.spectral_memory.clone()),
         ]);
         inputs
     }

crates/denoise/src/lib.rs

@@ -84,7 +84,7 @@ impl<S: Source> Denoiser<S> {
             .spawn(move || {
                 run_neural_denoiser(denoised_tx, input_rx);
             })
-            .unwrap();
+            .expect("Should be ablet to spawn threads");
 
         Ok(Self {
             inner: source,