fix: skip round+normalize when preserve_symmetry=True (already in [-1,1])

Author: FilyaGeikyan

vector_quantize_pytorch/finite_scalar_quantization.py

@@ -151,6 +151,9 @@ def quantize(self, z):
             offset = torch.rand_like(bounded_z) - 0.5
             bounded_z = torch.where(offset_mask, bounded_z + offset, bounded_z)
 
+        if preserve_symmetry:
+            return bounded_z
+        
         return round_ste(bounded_z) / half_width
 
     def _scale_and_shift(self, zhat_normalized):