perf(playback): optimize audio conversion with 16-bit dithering and bit shifts

Since Spotify audio is always 16-bit depth, optimize the conversion pipeline:
- Always dither at 16-bit level regardless of output format
- Preserve fractional precision until final rounding for better requantization
- Replace floating-point multiplication with compile-time bit shifts
- Add comprehensive inlining to eliminate function call overhead
- Specialize 24-bit clamping to remove runtime branching

This maintains proper dithering of the original 16-bit quantization artifacts
while maximizing performance through bit-shift operations and eliminating
unnecessary runtime calculations.

playback/src/dither.rs

@@ -64,6 +64,7 @@ impl Ditherer for TriangularDitherer {
         Self::NAME
     }
 
+    #[inline]
     fn noise(&mut self) -> f64 {
         self.distribution.sample(&mut self.cached_rng)
     }
@@ -98,6 +99,7 @@ impl Ditherer for GaussianDitherer {
         Self::NAME
     }
 
+    #[inline]
     fn noise(&mut self) -> f64 {
         self.distribution.sample(&mut self.cached_rng)
     }
@@ -130,6 +132,7 @@ impl Ditherer for HighPassDitherer {
         Self::NAME
     }
 
+    #[inline]
     fn noise(&mut self) -> f64 {
         let new_noise = self.distribution.sample(&mut self.cached_rng);
         let high_passed_noise = new_noise - self.previous_noises[self.active_channel];