PRX Set downscale_freq_shift to 0 for consistency with internal implementation (#12791)

fix timestepembeddings downscale_freq_shift to be consitant with Photoroom's original code

Author: DavidBert

src/diffusers/models/transformers/transformer_prx.py

@@ -694,6 +694,7 @@ def _compute_timestep_embedding(self, timestep: torch.Tensor, dtype: torch.dtype
                 max_period=self.time_max_period,
                 scale=self.time_factor,
                 flip_sin_to_cos=True,  # Match original cos, sin order
+                downscale_freq_shift=0.0,
             ).to(dtype)
         )